Architectures for batteries having two different chemistries

ABSTRACT

An automotive battery module having dual voltage is disclosed, including a housing and a plurality of battery cells connected to form battery cell blocks disposed in the housing. A battery control unit is provided disposed in the housing and is configured to control operation of a battery system. The battery system includes at least one switching device operably connected to a first battery cell block in a first connection arrangement. The first battery cell block is configured to deliver a first voltage. The switching device is also operably connected to a second battery cell block in a second connection arrangement. The second battery cell block is configured to deliver a second voltage. A plurality of terminals are provided on the housing and electrically coupled to the battery control unit and plurality of battery cells, providing an external electrical connection to deliver the first voltage and the second voltage.

CROSS-REFERENCE TO RELATED APPLICATIONS

Under 35 U.S.C. § 120, this application is a continuation of U.S. patentapplication Ser. No. 15/389,772 filed Dec. 23, 2016, which is acontinuation of U.S. patent application Ser. No. 14/161,858 filed Jan.23, 2014, which claims priority from and benefit of U.S. ProvisionalApplication No. 61/860,448 filed Jul. 31, 2013, each of which isincorporated herein by reference in their entireties for all purposes.

BACKGROUND

The present disclosure relates generally to the field of batteries andbattery systems. More specifically, the present disclosure relates tobattery systems that may be used in vehicular contexts, as well as otherenergy storage/expending applications.

This section is intended to introduce the reader to various aspects ofart that may be related to various aspects of the present disclosure,which are described and/or claimed below. This discussion is believed tobe helpful in providing the reader with background information tofacilitate a better understanding of the various aspects of the presentdisclosure. Accordingly, it should be understood that these statementsare to be read in this light, and not as admissions of prior art.

Vehicles generally use one or more battery systems to power features inthe vehicle including the air conditioning, radio, alarm system, andother electronics. To reduce the amount of undesirable emissionsproducts and improve the fuel efficiency of vehicles, improvements havebeen made to vehicle technologies. For example, some vehicles, such as amicro-hybrid vehicle, may disable the internal combustion engine whenthe vehicle is idling and utilize a battery system to continue poweringthe electronics as well as restarting (e.g., cranking) the engine whenpropulsion is desired. As used herein, the ability to disable the engineand restart the engine when a vehicle is idling is referred to as an“auto-stop” operation. Additionally, some vehicles may utilizetechniques, such as regenerative braking, to generate and storeelectrical power as the vehicle decelerates or coasts. Morespecifically, as vehicle reduces in speed, a regenerative braking systemmay convert mechanical energy into electrical energy, which may then bestored and/or used to power to the vehicle.

Thus, as vehicle technologies (e.g., auto-stop and regenerative brakingtechnology) continue to evolve, there is a need to provide improvedpower sources (e.g., battery systems or modules) for such vehicles. Forexample, it may be beneficial to improve the power storage and powerdistribution efficiency for such power sources.

SUMMARY

Certain embodiments commensurate in scope with the disclosed subjectmatter are summarized below. These embodiments are not intended to limitthe scope of the disclosure, but rather these embodiments are intendedonly to provide a brief summary of certain disclosed embodiments.Indeed, the present disclosure may encompass a variety of forms that maybe similar to or different from the embodiments set forth below.

The present disclosure relates to batteries and battery systems. Morespecifically, the present disclosure relates to various electrochemicaland electrostatic energy storage technologies (e.g. lead-acid batteries,nickel-zinc batteries, nickel-metal hydride batteries, and lithiumbatteries). Particular embodiments are directed to dual chemistrybattery modules that may be used in vehicular contexts (e.g.,micro-hybrid vehicles) as well as other energy storage/expendingapplications (e.g., energy storage for an electrical grid).

More specifically, the dual chemistry battery modules may include afirst battery utilizing a first battery chemistry and a second batteryutilizing a second battery chemistry. The first battery and the secondbattery may be connected in various parallel architectures, such aspassive, semi-passive, switch passive, semi-active, or activearchitectures. For example, in a passive architecture the first batteryand the second battery may be directly coupled to the terminals of thebattery module. To increase the amount of control over the batterymodule, in a semi-passive architecture, a switch may be included betweeneither the first battery or the second battery and the terminals of thebattery module. The switch may then be opened/closed to selectivelyconnect either the first battery or the second battery. In a switchpassive architecture, switches may be included between both the firstbattery and the second battery and the terminals of the battery module.Thus, the switches enable both the first battery and the second batteryto be controlled relatively independently. In a semi-activearchitecture, a DC/DC converter may be included between either the firstbattery or the second battery and the terminals of the battery module.The DC/DC converter may function to selectively connect either the firstbattery or the second battery and to enable the use of a constantvoltage alternator. In an active architecture, DC/DC converters may beincluded between both the first battery and the second battery and theterminals of the battery module. The DC/DC converters enable both thefirst battery and the second battery to be controlled relativelyindependently and the use of a constant voltage alternator.

Additionally, the battery chemistries used in the first battery and thesecond battery may be selected based on desired characteristics foreach. For example, the first battery may utilize a lead-acid chemistryto supply large surges of current, which may be utilized to start (e.g.,crank) an internal combustion engine. The second battery may utilizevarious battery chemistries (e.g., nickel manganese cobalt oxide,lithium manganese oxide/nickel manganese cobalt oxide, or lithiummanganese oxide/lithium titanate) with a higher coulombic efficiencyand/or a higher charge power acceptance rate (e.g., higher maximumcharging voltage or charging current) than the first battery. As usedherein, “coulombic efficiency” and “charge power acceptance rate” may beused interchangeably to describe charging efficiency. In other words,the second battery may be recharged more efficiently and at a fasterrate, for example while capturing regenerative power. Accordingly, insome embodiments, the first battery may be the primary source ofelectrical power and the second battery may supplement the firstbattery, for example by capturing, storing, and distributingregenerative power.

Accordingly, in a first embodiment, a battery system includes a firstbattery coupled directly to an electrical system, in which the firstbattery includes a first battery chemistry, and a second battery coupleddirectly to the electrical system in parallel with the first battery, inwhich second battery includes a second battery chemistry that has ahigher coulombic efficiency than the first battery chemistry. The secondbattery is configured to capture a majority of regenerative powergenerated during regenerative braking, and to supply the capturedregenerative power to power the electrical system by itself or incombination with the first battery.

In another embodiment, a battery system includes a first battery coupledto an electrical system, in which the first battery includes a firstbattery chemistry, and a second battery selectively coupled to theelectrical system via a switch and in parallel with the first battery,in which the second battery includes a second battery chemistry that hasa higher coulombic efficiency than the first battery chemistry. Theswitch is configured to couple the second battery to the electricalsystem to enable the second battery to capture a majority ofregenerative power generated during regenerative braking and to enablethe second battery to supply the regenerative power to power theelectrical system by itself or in combination with the first battery.

In another embodiment, a battery system includes a first batteryselectively coupled to an electrical system via a switch, in which thefirst battery includes a first battery chemistry, and a second batterydirectly coupled to the electrical system in parallel with the firstbattery, in which the second battery includes a second battery chemistrythat has a higher charge power acceptance rate than the first batterychemistry. The switch is configured to disconnect the first battery fromthe electrical system to enable the second battery to be charged at avoltage higher than the first battery maximum charging voltage duringregenerative braking.

In another embodiment, a battery system includes a first battery coupledto an electrical system, in which the first battery includes a firstbattery chemistry, and a second battery selectively coupled to theelectrical system via a DC/DC converter and in parallel with the firstbattery, in which the second battery includes a second battery chemistrythat has a higher coulombic efficiency and/or a higher charge poweracceptance rate than the first battery chemistry. The DC/DC converter isconfigured to couple the second battery to the electrical system toenable the second battery to capture a majority of regenerative powergenerated during regenerative braking and to enable the second batteryto supply the regenerative power to power the electrical system byitself or in combination with the first battery.

BRIEF DESCRIPTION OF TEE DRAWINGS

These and other features, aspects, and advantages of the presentdisclosure will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is a perspective view of a vehicle (e.g., a micro-hybridvehicle), in accordance with an embodiment of the present approach;

FIG. 2 is a schematic view of the vehicle depicted in FIG. 1illustrating power distribution through the vehicle, in accordance withan embodiment of the present approach;

FIG. 3 is a schematic view of a battery system with a first battery anda second battery, in accordance with an embodiment of the presentapproach;

FIG. 4 is a graph illustrating voltage characteristics for variousbattery chemistries, in accordance with an embodiment of the presentapproach;

FIG. 5 is a graph illustrating voltage characteristics of non-voltagematched battery chemistries, in accordance with an embodiment of thepresent approach;

FIG. 6 is a graph illustrating voltage characteristics of partialvoltage matched battery chemistries, in accordance with an embodiment ofthe present approach;

FIG. 7 is a graph illustrating voltage characteristics of voltagematched battery chemistries, in accordance with an embodiment of thepresent approach;

FIG. 8 is a schematic diagram of a passive battery architecture, inaccordance with an embodiment of the present approach;

FIG. 9 is a graph describing various hypothetical operations of avehicle over time, in accordance with an embodiment of the presentapproach;

FIG. 10A is a graph illustrating the voltage of a passive battery systemwith non-voltage matched battery chemistries for the vehicle describedin FIG. 9, in accordance with an embodiment of the present approach;

FIG. 10B is a graph illustrating the voltage of a first embodiment of apassive battery system with partial voltage matched battery chemistriesfor the vehicle described in FIG. 9, in accordance with an embodiment ofthe present approach;

FIG. 10C is a graph illustrating the voltage of a second embodiment of apassive battery system with partial voltage matched battery chemistriesfor the vehicle described in FIG. 9, in accordance with an embodiment ofthe present approach;

FIG. 10D is a graph illustrating the voltage of a passive battery systemwith voltage matched battery chemistries for the vehicle described inFIG. 9, in accordance with an embodiment of the present approach;

FIG. 11A is a schematic diagram of a semi-passive battery architecturewith a switch to selectively connect a first battery, in accordance withan embodiment of the present approach;

FIG. 11B is a schematic diagram of a semi-passive battery architecturewith a switch to selectively connect a second battery, in accordancewith an embodiment of the present approach;

FIG. 12A is a graph illustrating the voltage of a semi-passive batterysystem with non-voltage matched battery chemistries for the vehicledescribed in FIG. 9, in accordance with an embodiment of the presentapproach;

FIG. 12B is a graph illustrating the voltage of a first embodiment of asemi-passive battery system with partial voltage matched batterychemistries for the vehicle described in FIG. 9, in accordance with anembodiment of the present approach;

FIG. 12C is a graph illustrating the voltage of a second embodiment of asemi-passive battery system with partial voltage matched batterychemistries for the vehicle described in FIG. 9, in accordance with anembodiment of the present approach;

FIG. 12D is a graph illustrating the voltage of a semi-passive batterysystem with voltage matched battery chemistries for the vehicledescribed in FIG. 9, in accordance with an embodiment of the presentapproach;

FIG. 13 is a schematic diagram of a switch-passive battery architecture,in accordance with an embodiment of the present approach;

FIG. 14A is a graph illustrating the voltage of a switch passive batterysystem with non-voltage matched battery chemistries for the vehicledescribed in FIG. 9, in accordance with an embodiment of the presentapproach;

FIG. 14B is a graph illustrating the voltage of a first embodiment of aswitch passive battery system with partial voltage matched batterychemistries for the vehicle described in FIG. 9, in accordance with anembodiment of the present approach;

FIG. 14C is a graph illustrating the voltage of a third embodiment of aswitch passive battery system with partial voltage matched batterychemistries for the vehicle described in FIG. 9, in accordance with anembodiment of the present approach;

FIG. 14D is a graph illustrating the voltage of a switch passive batterysystem with voltage matched battery chemistries for the vehicledescribed in FIG. 9, in accordance with an embodiment of the presentapproach;

FIG. 15A is a schematic diagram of a semi-active battery architecturewith a DC/DC converter to selectively connect a lead-acid battery, inaccordance with an embodiment of the present approach;

FIG. 15B is a schematic diagram of a semi-active battery architecturewith a DC/DC converter to selectively connect a second battery, inaccordance with an embodiment of the present approach;

FIG. 16 is a block diagram of a first embodiment of a DC-DC converterwith a bypass path for the semi-active or active architecture, inaccordance with an embodiment of the present approach;

FIG. 17 is a block diagram of a second embodiment of a DC-DC converterwith a bypass path for the semi-active or active architecture, inaccordance with an embodiment of the present approach;

FIG. 18A is a graph illustrating the voltage of a semi-active batterysystem with non-voltage matched battery chemistries for the vehicledescribed in FIG. 9, in accordance with an embodiment of the presentapproach;

FIG. 18B is a graph illustrating the voltage of a first embodiment of asemi-active battery system with partial voltage matched batterychemistries for the vehicle described in FIG. 9, in accordance with anembodiment of the present approach;

FIG. 18C is a graph illustrating the voltage of a third embodiment of asemi-active battery system with partial matched battery chemistries forthe vehicle described in FIG. 9, in accordance with an embodiment of thepresent approach;

FIG. 18D is a graph illustrating the voltage of a semi-active batterysystem with voltage matched battery chemistries for the vehicledescribed in FIG. 9, in accordance with an embodiment of the presentapproach;

FIG. 19 is a schematic diagram of an active battery architecture, inaccordance with an embodiment of the present approach;

FIG. 20A is a graph illustrating the voltage of an active battery systemwith non-voltage matched battery chemistries for the vehicle describedin FIG. 9, in accordance with an embodiment of the present approach;

FIG. 20B is a graph illustrating the voltage of a first embodiment of anactive battery system with partial voltage matched battery chemistriesfor the vehicle described in FIG. 9, in accordance with an embodiment ofthe present approach;

FIG. 20C is a graph illustrating the voltage of a third embodiment of anactive battery system with partial voltage matched battery chemistriesfor the vehicle described in FIG. 9, in accordance with an embodiment ofthe present approach;

FIG. 20D is a graph illustrating the voltage of an active battery systemwith voltage matched battery chemistries for the vehicle described inFIG. 9, in accordance with an embodiment of the present approach; and

FIG. 21 is a schematic diagram of a switch-active battery architecture,in accordance with an embodiment of a present approach.

DETAILED DESCRIPTION

One or more specific embodiments of the present techniques will bedescribed below. In an effort to provide a concise description of theseembodiments, not all features of an actual implementation are describedin the specification. It should be appreciated that in the developmentof any such actual implementation, as in any engineering or designproject, numerous implementation-specific decisions must be made toachieve the developers' specific goals, such as compliance withsystem-related and business-related constraints, which may vary from oneimplementation to another. Moreover, it should be appreciated that sucha development effort might be complex and time consuming, but wouldnevertheless be a routine undertaking of design, fabrication, andmanufacture for those of ordinary skill having the benefit of thisdisclosure.

As discussed above, vehicle technology has improved to increase fueleconomy and/or reduce undesirable emissions compared to more traditionalgas-powered vehicles. For example, micro-hybrid vehicles disable thevehicle's internal combustion engine when the vehicle is idling. Whilethe vehicle's internal combustion engine is disabled, the battery systemmay continue supplying power to the vehicle's electrical system, whichmay include the vehicle's radio, air conditioning, electronic controlunits, and the like. Additionally, regenerative braking vehicles captureand store electrical power generated when the vehicle is braking orcoasting. In some embodiments, the generated electrical power may thenbe utilized to supply power to the vehicle's electrical system. In otherembodiments, the generated electrical power may be utilized to stabilizevoltage during high demand, for example in regenerative storage systems.

Based on the advantages over traditional gas-power vehicles,manufactures, which generally produce traditional gas-powered vehicles,may desire to utilize improved vehicle technologies (e.g., micro-hybridtechnology or regenerative braking technology) within their vehiclelines. These manufactures often utilize one of their traditional vehicleplatforms as a starting point. Generally, traditional gas-poweredvehicles are designed to utilize 12 volt battery systems (e.g., voltagebetween 7-18 volts), such as a single 12 volt lead-acid battery.Accordingly, the single lead-acid battery may be adapted for theimproved vehicle technologies. For example, the lead-acid battery may beutilized to capture and store regenerative power and/or supply power tothe electrical system during auto-stop. However, in some embodiments, alead-acid battery may be less efficient at capturing regenerativeelectrical power due to the lower coulombic efficiency and/or lowercharge power acceptance rate associated with the lead-acid batterychemistry. As used herein, “coulombic efficiency” and “charge poweracceptance rate” may be used interchangeably to describe chargingefficiency and charging rate. Additionally, the lead-acid batterycapacity may be increased to account for the electrical power demandduring auto-stop, which may increase cost. As such, it would bebeneficial to improve the efficiency of the power storage in the batterysystem and the efficiency of the power distribution to the vehicle'selectrical system while largely conforming with existing vehicleelectrical systems.

Accordingly, present embodiments include physical battery systemfeatures, and so forth, that facilitate providing improved 12 voltbattery systems. As used herein, a “12 volt battery system” is intendedto describe a battery system that supplies between 7-18 volts to anelectrical system. For example, in some embodiments, the battery modulemay include multiple differing battery chemistries to improve thestorage and distribution efficiency of the battery module. Morespecifically, as will be described in more detail below, the batterymodule may include a first battery (e.g., primary battery) with a firstbattery chemistry and a second battery (e.g., secondary battery) with asecond battery chemistry. As used herein, “battery” is intended describeenergy storage devices that utilize various chemical reactions to storeand/or distribute electrical power. In some embodiments, the firstbattery and the second battery may operate in tandem. For example, thefirst (e.g., primary) battery may efficiently supply large amounts ofcurrent, for example to crank the internal combustion engine, and thesecond battery (e.g., power device) may efficiently capture and storepower generated due to its higher coulombic efficiency and/or higherpower charge acceptance rate. Additionally, the power stored in thesecond battery may be expended to provide power to the vehicle'selectrical system. In other words, the first battery may be the primarysource of electrical power and the second battery may supplement thebattery, which in some embodiments may enable the storage capacityand/or the overall physical dimensions of the battery module to bereduced.

To facilitate supplementing the first battery with the second battery,the first battery and the second battery may be connected in variousparallel architectures. For example, the battery module may utilize apassive architecture, a semi-passive architecture, a switch passivearchitecture, a semi-active architecture, or an active architecture. Aswill be described in more detail below, in a passive architecture, thefirst battery and the second battery may be directly coupled to theterminals of the battery module, which may reduce the complexity of acontrol algorithm for the battery system. In a semi-passivearchitecture, one of the first battery and the second battery may becoupled to the terminals of the battery module via a switch while theother may be directly coupled. In some embodiments, the switch mayincrease the control over operation of the battery module by enablingeither the first battery or the second battery to be selectivelyconnected/disconnected. In a switch passive architecture, both the firstbattery and the second battery may be coupled to the terminals of thebattery module via switches. In some embodiments, the switches mayfurther increase the control over operation of the battery module byenabling both the first battery and the second battery to be controlled(e.g., connected/disconnected) relatively independently. In otherembodiments, the switches may be replaced by DC/DC converters to enablethe use of a constant voltage alternator. For example, in a semi-activearchitecture, one of the first battery or the second battery is coupledto the terminals of the battery module via a DC/DC converter. In anactive architecture, both the first battery and the second battery maybe coupled to the terminals of the battery module via DC/DC converters.In some embodiments, utilizing the techniques described herein mayincrease fuel economy and reduce undesirable emissions by 3-5% ascompared to auto-stop technology utilizing traditional 12 volt batterysystems (e.g., a single 12 volt lead-acid battery) because the load onthe alternator is reduced by more efficiently capturing regenerativepower.

With the foregoing in mind, FIG. 1 is a perspective view of anembodiment of a vehicle 10, such as a micro-hybrid vehicle. Although thefollowing discussion is presented in relation to micro-hybrid vehicles,the techniques described herein may be applied to other vehiclesincluding electrical-powered and gas-powered vehicles. As discussedabove, it would be desirable for a battery system 12 to be largelycompatible with traditional vehicle designs. Accordingly, the batterysystem 12 may be placed in a location in the micro-hybrid vehicle 10that would have housed the traditional battery. For example, asillustrated, the micro-hybrid vehicle 10 may include the battery system12A positioned similarly to a lead-acid battery of a typicalcombustion-engine vehicle (e.g., under the hood of the vehicle 10). Byfurther example, in certain embodiments, the micro-hybrid vehicle 10 mayinclude the battery system 12B positioned near a center of mass of themicro-hybrid vehicle 10, such as below the driver or passenger seat. Bystill further example, in certain embodiments, the micro-hybrid vehicle10 may include the battery system 12C positioned below the rearpassenger seat or near the trunk of the vehicle. It should beappreciated that, in certain embodiments, positioning a battery system12 (e.g., battery system 12B or 12C) in or about the interior of thevehicle may enable the use of air from the interior of the vehicle tocool the battery system 12 (e.g., using a heat sink or a forced-aircooling design).

To simplify discussion of the battery system 12, the battery system 12will be discussed in relation to the battery system 12A disposed underthe hood of the vehicle 10, as depicted in FIG. 2. As depicted, thebattery system 12 includes a battery module 14 coupled to an ignitionsystem 16, an internal combustion engine 18, and a regenerative brakingsystem 20. More specifically, the battery module 14 may supply power tothe ignition system 16 to start (i.e., crank) the internal combustionengine 18. In some embodiments, the ignition system 16 may include atraditional starter and/or a belt starter generator (BSG). Theregenerative braking system 20 may capture energy to charge the batterymodule 14. In some embodiments, the regenerative braking system 20 mayinclude an alternator, such as a belt starter generator (BSG), one ormore electric motors, to convert mechanical energy into electricalenergy, and/or control components.

Furthermore, as described above, the battery system 12 may supply powerto components of the vehicle's electrical system. For example, thebattery system 12 may supply power to the radiator cooling fans, climatecontrol system, electric power steering systems, active suspensionsystems, auto park systems, electric oil pumps, electricsuper/turbochargers, electric water pumps, heated windscreen/defrosters,window lift motors, vanity lights, tire pressure monitoring systems,sunroof motor controls, power seats, alarm systems, infotainmentsystems, navigation features, lane departure warning systems, electricparking brakes, external lights, or any combination thereof.Illustratively, the battery system 12 depicted in FIG. 2 supplies powerto a heating, ventilation, and air conditioning (HVAC) system 22 and avehicle console 24.

To facilitate supply of power from the battery system 12 to the variouscomponents in vehicle's electrical system (e.g., HVAC system 22 andvehicle console 24), the battery module 14 includes a first terminal 26and a second terminal 28. In some embodiments, the second terminal 28may provide a ground connection and the first terminal 26 may provide apositive voltage ranging between 7-18 volts. A more detailed view of anembodiment of a battery module 14 is depicted in FIG. 3. As previouslynoted, the battery module 14 may have dimensions comparable to those ofa typical lead-acid battery to limit modifications to the vehicle 10design to accommodate the battery system 12. For example, the batterymodule 14 may be of similar dimensions to an H6 battery, which may beapproximately 13.9 inches×6.8 inches×7.5 inches. As depicted, thebattery module 14 may be included within a single continuous housing. Inother embodiments, the battery module 14 may include multiple housingscoupled together (e.g., a first housing including the first battery anda second housing including the second battery).

As depicted, the battery module 14 includes the first terminal 26, thesecond terminal 28, a first battery (e.g., a lead acid battery) 30, asecond battery 32, and a battery control unit 34. As used herein, the“battery control unit” generally refers to control components thatcontrol operation of the battery system 12, such as switches within thebattery module or an alternator. The operation of the battery module 14may be controlled by the battery control unit 34. For example, thebattery control unit 34 may regulate (e.g., restrict or increase) poweroutput of each battery in the battery module 14, perform load balancingbetween the batteries, control charging and discharging of the batteries(e.g., via switches or DC/DC converters), determine a state of charge ofeach battery and/or the entire battery module 14, activate an activecooling mechanism, and the like. Accordingly, the battery control unit34 may include at least one memory 35 and at least one processor 37programmed to execute control algorithms for performing such tasks.Additionally, as depicted, the battery control unit 34 may be includedwithin the battery module 14. In other embodiments, the battery controlunit 34 may be included separate from the battery module 14, such as astandalone module.

Furthermore, as depicted, the first battery 30 and the second battery 32are connected in parallel across the first terminal 26 and the secondterminal 28 to enable charging and discharging of the batteries. Asdescribed above, the battery terminals 26 and 28 may output the powerstored in the battery module 14 to provide power to the vehicle'selectrical system. Additionally, the battery terminals 26 and 28 mayalso input power to the battery module 14 to enable the first battery 30and the second battery 32 to charge, for example, when the alternatorgenerates electrical power through regenerative braking.

As depicted in FIG. 3, the first battery 30 and the second battery 32are separate, which enables each to be configured based on desiredcharacteristics, such as output voltage. For example, the output voltageof the first battery 30 and second battery 32 may depend on theconfiguration of battery cells 36 within each (e.g., in serial orparallel) and the battery chemistries selected. As will be described inmore detail below, the configuration of battery cells and the batterychemistries selected may cause different voltage characteristics (e.g.,non-voltage matched, partial voltage matched, or voltage matched). Morespecifically, the differing voltage characteristics may cause the firstbattery 30 and the second battery 32 to operate differently in thevarious architectures (e.g., passive, semi-passive, switch passive,semi-active, or active) described herein.

Examples of various chemistries that may be utilized for the firstbattery 30 and second battery 32 are described in Table 1 below. Table 1is merely illustrative and is not intended as an exhaustive list ofbattery chemistries. Other battery chemistries that exhibit similarcharacteristics may also be utilized for the techniques describedherein.

TABLE 1 Battery Cell Chemistry Characteristics NMC LTO/NMC LTO/LMO NiMHNiZn LFP PbA Nominal Voltage V 3.6-3.75 2.5 2.51 1.2 1.65 3.3 12 MinVoltage V 2.4-3.0 2 1.5 1 1.1 2.5 8 Max Voltage V 4.1-4.3 2.8 2.8 1.51.9 3.65 18 Average Capacity (C rate, 20° C.) Ah 3.8-5.5 3.5 3.3 6.539-40 2.3 64-75

Table 1 describes the characteristics of a single lithium nickelmanganese cobalt oxide (NMC), lithium-titanate/lithium nickel manganesecobalt oxide (LTO/NMC), lithium-titanate/lithium manganese oxide(LTO/LMO), nickel-metal hydride (NiMH), nickel-zinc (NiZn), lithium ironphosphate (LFP) battery cells. More specifically, NMC battery chemistryrefers to a graphite anode with a lithium nickel manganese cobalt oxidecathode, the LTO/NMC battery chemistry refers to a lithium-titanateanode with a lithium manganese oxide cathode, the LTO/LMO batterychemistry refers to a lithium-titanate anode with a lithium manganeseoxide cathode, and the LFP battery chemistry refers to a graphite anodewith a lithium iron phosphate cathode. Additionally, Table 1 describesthe characteristics of a 12-volt lead-acid (PbA) battery.

As described above, the battery chemistries utilized in the firstbattery 30 and the second battery 32 may be selected based on desiredcharacteristics. In some embodiments, a battery chemistry selected forthe second battery 32 may have a higher coulombic efficiency and/or ahigher power charge acceptance rate (e.g., higher maximum charge currentor charge voltage) to improve the capture, storage, and/or distributionefficiency of the battery system 12. For example, the NMC batterychemistry due to its higher maximum charging voltage (e.g., 16.8 voltswhen four in series) and its higher maximum charging current (e.g., 200A) may be selected to reduce the recharge time of the second battery 32.As used herein, “maximum charging voltage” is intended to describe avoltage above which may negatively affect the battery. Illustratively,the maximum charging voltage of a lead-acid battery may be 14.8 voltsbecause when charged at a higher voltage (e.g., 16.8 volts) thelead-acid battery may begin gassing (e.g., producing hydrogen gas and/oroxygen gas), which may negatively affect the lifespan of the lead-acidbattery. Furthermore, the chemistry selected for the first battery 30may have a high energy density (e.g., lead-acid) and the chemistryselected for the secondary battery (e.g., power device) may have a highpower density.

Moreover, as described above, the battery cells 36 may be arranged(e.g., in serial or parallel) to achieve desired characteristics. Forexample, when four NMC battery cells are arranged in series, theresulting nominal voltage is 14.63 volts, which corresponds with the NMCvoltage curve 38 depicted in FIG. 4. More specifically, FIG. 4 is an XYplot that describes the voltage of a first battery 30 or second battery32, utilizing various battery chemistries, over the battery's totalstate of charge range (e.g., from 0% state of charge to 100% state ofcharge), in which state of charge is shown on the X-axis and voltage isshown on the Y-axis.

In addition to describing the voltage characteristics for an NMCbattery, FIG. 4 also describes the open circuit (e.g., static) voltagecharacteristics (e.g., open circuit voltage ranges) for the abovedescribed battery chemistries. More specifically, FIG. 4 also depicts aLTO/NMC voltage curve 40, a NiMH voltage curve 42, a LFP voltage curve44, a LTO/LMO voltage curve 46, a NiZn voltage curve 48, and a PbAvoltage curve 50. As discussed above, battery cells 36 (e.g., a NMCbattery cell, a LTO/LMO battery cell, or a LTO/NMC battery cell) may bearranged within each battery 30 or 32 to have characteristicscorresponding with the curves (e.g., NMC voltage curve 38, LTO/NMCvoltage curve 40, or LTO/LMO voltage curve 46) depicted in FIG. 4.Additionally, because voltages range between 8-17 volts, a dualchemistry battery module utilizing the battery chemistries described inFIG. 4 may generally conform with a 12 volt battery system. In otherwords, the dual chemistry battery module may supply power to anelectrical system designed to be powered by a traditional 12 voltbattery system, such as a single 12 volt lead-acid battery.

Based on the battery voltage curves depicted in FIG. 4, different pairsof battery chemistries may be selected. In other words, a first batterychemistry may be selected for the first battery 30 and a second batterychemistry may be selected for the second battery 32. Depending on thechemistry pairings, the battery module 14 may function differently. Morespecifically, the chemistry pair selected may cause the first battery 30and the second battery 32 to be non-voltage matched, partial voltagematched, or voltage matched. As used herein, “non-voltage matched” isintended to describe when the first battery 30 and the second battery 32open circuit voltage ranges do not overlap, “partial voltage matched” isintended to describe when the first battery 30 and the second battery 32open circuit voltage ranges partially overlap, for example when thevoltage overlap corresponds to between 1-74% of the second battery'stotal state of charge range, and “voltage matched” is intended todescribe when the first battery 30 and the second battery 32 voltageslargely overlap, for example when the voltage overlap corresponds tobetween 75-100% of the second battery's total state of charge range. Itshould be noted that as described above, the second battery 32 has ahigher coulombic efficiency and/or a higher charge power acceptance ratethan the first battery 30. In other words, the battery pairingcharacteristics are described based on the relationship of the highercoulombic efficiency and/or a higher charge power acceptance ratebattery (e.g., second battery) to the other battery (e.g., firstbattery).

Illustratively, voltage curves for an example of non-voltage matchedbatteries is depicted in FIG. 5, voltage curves for an example ofpartial voltage matched batteries is depicted in FIG. 6, and voltagecurves for an example of voltage matched batteries is depicted in FIG.7, which each is an XY plot depicting battery voltage curves from FIG.4. To simplify the following discussion, the first battery 30 will bedescribed as a lead-acid battery and the second battery 32 will bedescribed as a battery that utilizes the one of the other batterychemistries described above. As described will be described in moredetail below, the voltage of each battery may vary with its state ofcharge (SOC). For example, a lead-acid battery 30 at 0% state of chargemay have a voltage of 11.2 volts, at 50% state of charge may have avoltage of 12.2 volts, and at 100% state of charge may have a voltage of12.9 volts. In other words, the lead-acid battery has a voltage range of11.2-12.9 volts. Although the following discussion is made in referenceto a lead-acid battery and a second battery, the present techniques maybe applied to other battery pairings that have the same characteristics(e.g., non-voltage matched, partial voltage matched, or non-voltagematched).

As depicted in FIG. 5, when the second battery 32 is a NMC battery, thelead-acid battery 30 and the second battery 32 are non-voltage matchedbecause at no point do the PbA voltage curve 50 and the NMC voltagecurve 38 overlap. In other words, regardless of their respective stateof charge (SOC), the open circuit voltage of the lead-acid battery 30and the second battery 32 voltages do not overlap. To help illustrate,the lead-acid battery 30 has an open circuit voltage range of 11.2-12.9volts and the NMC battery 32 has an open circuit voltage range between13.3-16.4 volts. Accordingly, when the second battery 32 is at itslowest voltage (e.g., at 0% state of charge), its voltage isapproximately 13.3 volts. On the other hand, when the lead-acid battery30 is at its highest voltage (e.g., 100% state of charge), its voltageis approximately 12.9 volts. In other embodiments, the batteries mayalso be non-voltage matched when the second battery 32 is a LithiumNickel Cobalt Aluminum Oxide (NCA) (e.g., NCA cathode with graphiteanode) or NMC-NCA battery (e.g., blended NMC-NCA cathode with graphiteanode).

As depicted in FIG. 6, when the second battery 32 is a LTO/NMC battery,the lead-acid battery 30 and the second battery 32 are partial voltagematched because the PbA voltage curve 50 and the LTO/NMC voltage curve40 partially overlap. In other words, depending on their respectivestates of charge, the open circuit voltage of the lead acid battery 30and the second battery 32 may be the same. To help illustrate, thelead-acid battery 30 has an open circuit voltage range of 11.2-12.9volts and the LTO/NMC battery 32 has an open circuit voltage rangebetween 11.8-16 volts. As described above, the battery 30 and the secondbattery 32 may be partial voltage matched when the voltage overlapcorresponds to between 1-74% of the second battery's total state ofcharge range. In the depicted embodiment, the first battery 30 and thesecond battery 32 may overlap between 11.8-12.9 volts. For example, whenthe second battery 32 is at a 20% state of charge and the lead-acidbattery 30 is at a 100% state of charge, both will have a voltage ofapproximately 12.9 volts. In other words, the voltages may overlap whenthe second battery 32 is between 0-20% state of charge (e.g., 20% of thetotal state of charge range). Based on the battery voltage curvesdepicted in FIG. 4, in other embodiments, the batteries 30 and 32 mayalso be partial voltage matched when the second battery 32 is a NiMH orLFP battery. In other embodiments, the batteries may also be non-voltagematched when the second battery 32 is a LTO/NMC-LMO battery (e.g.,NMC-LMO cathode with LTO anode).

As depicted in FIG. 7, when the second battery 32 is a LTO/LMO battery,the lead-acid battery 30 and the second battery 32 are voltage matchedbecause the PbA voltage curve 50 and the LTO/LMO voltage curve 46largely overlap. In other words, the open circuit voltage of thelead-acid battery 30 and the open circuit voltage of the second battery32 may be the same for most of their respective states of charge. Tohelp illustrate, the lead-acid battery 30 has an open circuit voltagerange of 11.2-12.9 volts and the LTO/NMC battery 32 has an open circuitvoltage range between 11.5-13.3 volts. As described above, the lead-acidbattery 30 and the second battery 32 may be voltage matched when thevoltage overlap corresponds to between 75-100% of the second battery'stotal state of charge range. In the depicted embodiment, the firstbattery 30 and the second battery 32 may overlap between 11.5-12.9volts. For example, when the second battery 32 is at a 75% state ofcharge and the lead-acid battery 30 is at 100% state of charge, bothwill have a voltage of approximately 12.9 volts. In other words, thevoltages may overlap when the second battery 32 is between 0-75% stateof charge (e.g., 75% of the total state of charge range). Based on thevoltage curves depicted in FIG. 4, in other embodiments, the batteries30 and 32 may also be voltage matched when the second battery is a NiZnbattery.

As will be described in more detail below, the voltage pairing (e.g.,non-voltage match, partial-voltage match, or voltage match) selected maydetermine the operation of the batteries 30 and 32 within the vehicle.Additionally, as described above, the lead-acid battery 30 and thesecond battery 32 are connected in various parallel architectures withinthe battery module 14. Accordingly, when the battery module 14 isconnected to the vehicle 10, the lead-acid battery 30 and the secondbattery 32 are also connected in parallel with the rest of the vehicle,such as the ignition system 16, the regenerative braking system 20, andthe vehicle's electrical system.

More specifically, as described above, the lead-acid battery 30 and thesecond battery 32 may utilize various parallel architectures including apassive architecture, a semi-passive architecture, a switch-passivearchitecture, a semi-active architecture, an active architecture, or aswitch active architecture. As will be described in more detail below,one embodiment of a passive architecture 52 is depicted in FIG. 8,embodiments of a semi-passive architecture 54 are depicted in FIGS. 11Aand B, one embodiment of a switch-passive architecture 56 is describedin FIG. 13, embodiments of a semi-active architecture 58 are describedin FIGS. 15A and B, and one embodiment of an active architecture 60 isdepicted in FIG. 19. As depicted in each architecture, the lead-acidbattery 30 and the second battery 32 are coupled in parallel with astarter (e.g., ignition system) 62, an alternator (e.g., regenerativebraking system) 64, and the vehicle's electrical system 66 via a bus 68.Additionally, the lead-acid battery 30 and the second battery 32 areselectively connected to the starter 62 via a switch 70. As can beappreciated, the switch 70 may represent the various mechanisms, such assolenoids, that enable the lead-acid battery 30 and/or the secondbattery 32 to start (e.g., crank) the internal combustion engine. Aswill be described in more detail below, the differences between each ofthe architectures is the amount of control over the operation of each ofthe lead-acid battery 30 and the second battery 32.

To help illustrate the functional differences between each of thearchitectures (e.g., passive, semi-passive, switch-passive, semi-active,and active), each architecture will be described in relation to ahypothetical operation of the vehicle 10 as described in FIG. 9. FIG. 9is an XY plot that describes various vehicle operations between time 0and time 8, in which the Y-axis is vehicle speed and the X-axis is time(i.e., time 0 to time 8). More specifically, between time 0 and time 1,the vehicle 10 is key-off 72. As used herein, “key-off” is intended todescribe when an operator (e.g., a driver) is not using the vehicle 10.For example, key-off 72 may describe when the vehicle 10 is parked in agarage overnight. During key-off 72, the internal combustion engine 18is disabled and the battery system 12 continues to provide power tocomponents of the vehicle's electrical system 66 that remain inoperation even when the operator is away, such as the alarm system orengine control unit. Accordingly, as depicted, the vehicle has no speed.

At time 1, the vehicle 10 is cold cranked 74. As used herein, “coldcrank” is intended to describe when an operator starts (i.e., cranks)the internal combustion engine 18 from key-off 72. Accordingly, duringcold crank 74, the battery system 12 supplies power to the ignitionsystem 16 (e.g., starter 62) to start the internal combustion engine 18.After the internal combustion engine 18 is started, between time 1 and2, the vehicle 10 accelerates 76. Accordingly, as depicted, the vehicle10 increases speed. Between time 2 and time 3, the vehicle 10 cruises78. Accordingly, as depicted, the vehicle 10 remains at a relativelyconstant speed. While the vehicle 10 accelerates 76 and cruises 78, thebattery system 12 supplies power to the vehicle's electrical system 66,which may include the HVAC system 22 and the vehicle console 24. Torecharge the battery system 12, the alternator 64 may periodically beturned on, which as will be described in more detail below may result inmicro-cycles. It should be noted that the embodiments described belowmay micro-cycle a battery 30 or 32 to achieve a target state charge;however additionally or alternatively, in other embodiments, thealternator 64 may supply power directly to the vehicle's electricalsystem 66 while the vehicle 10 is accelerating 76 and/or cruising 78without micro-cycling the battery 30 or 32. In other words, thealternator 64 may supply power directly to the vehicle's electricalsystem, for example while the vehicle 10 accelerates 76 or cruises 78.

Between time 3 and time 4, the vehicle 10 decelerates and generateselectrical power via regenerative braking 80. Accordingly, as depicted,the vehicle 10 reduces speed. More specifically, the kinetic energy(e.g., motion of the vehicle) is converted into electrical power throughthe alternator 64. The generated electrical power may be stored by thebattery system 12 and/or distributed to supply power to the vehicle'selectrical system 66. As will be described in more detail below,depending on the configuration of the battery system 12, the generatedelectrical power may be stored in and distributed from the battery 30,the second battery 32, or both. Between time 4 and time 5, the vehicle10 again cruises 82, and between time 5 and 6, the vehicle 10 againdecelerates and generates electrical power via regenerative braking 84.

Between time 6 and time 7, the vehicle 10 enters auto-stop 86. Asdescribed above, during auto-stop 86, the internal combustion engine 18is disabled while the vehicle 10 is idle. Accordingly, as depicted, thevehicle has no speed. From auto-stop 86, to resume driving the vehicle,the battery system 12 warm cranks 88 the internal combustion engine 18.As used herein, “warm crank” is intended to refer to starting (i.e.,cranking) the internal combustion engine 18 from auto-stop 86. As willbe described further below, the power used to warm crank 88 the internalcombustion engine 18 may be less than the power to cold crank 74. Afterthe internal combustion engine 18 is started (i.e., cranked), thevehicle 10 again accelerates 90 between time 7 and time 8.

While the vehicle is in auto-stop 86, the battery system 12 continues tosupply power to the vehicle's electrical system 66. Additionally, thismay include supplying power to the starter 62 to warm crank 88 theinternal combustion engine 18. However, while in auto-stop 86, becausethe internal combustion engine 18 is disabled, the battery system 12 isnot charged by the alternator 64. Accordingly, as described above, itmay be beneficial to improve the efficiency of the battery system 12 instoring (e.g., capturing) generated electrical power during regenerativebraking (e.g., 80 or 84). Additionally, it may be beneficial to improvethe efficiency of the battery system in distributing (e.g., supplying)stored electrical power during various vehicle operations (e.g.,cruising 82, auto-stop 86, warm cranking 88, and/or acceleration 90).

As discussed above, to help illustrate the difference between each ofthe architectures (e.g., passive, semi-passive, switch passive,semi-active, active), the operation of battery systems 12 utilizing eachof the architectures will be described below with regard to thehypothetical vehicle operation described in FIG. 9. Additionally, foreach of the architectures, different battery chemistry configurations(e.g., non-voltage match, partial voltage match, voltage match) will bedescribed. Furthermore, to simplify the following discussion, thebattery system 12 will be discussed in relation to a battery module 14that includes both the lead-acid battery 30 and the second battery 32.However, in other embodiments, the lead-acid battery 30 and the secondbattery 32 may be located in different regions of the vehicle 10, forexample as separate modules.

Passive Architectures for Dual Chemistry Batteries

Returning to FIG. 8, a passive battery system 52 is depicted. Asdepicted, the lead-acid battery 30 and the second battery 32 aredirectly coupled to the bus 68. Accordingly, the operation of thebattery 30 and the second battery 32 may be controlled by thecharacteristics of each of the batteries. More specifically, thecharging and discharging of the batteries 30 and 32 may be controlled bythe current steering characteristics (e.g., internal resistance) of thelead-acid battery 30 and the second battery 32. For example, when thelead-acid battery 30 is fully charged or close to fully charged (e.g.,generally full state of charge), the lead-acid battery 30 may have ahigh internal resistance that steers current toward the second battery32. On the other hand, when the lead-acid battery 30 is less fullycharged, the current may be shared between the lead-acid battery 30 andthe second battery 32. In other words, the internal resistance may beproportionally related to the battery state of charge (e.g., high stateof charge high internal resistance). Additionally, when the secondbattery 32 has higher open circuit voltage than the first battery 30,the second battery 32 may provide power by itself, for example to theelectrical system 66, until it nears the open circuit voltage of thefirst battery. The exact voltage when the first battery 30 may beginproviding power may be based on the various factors, such as theinternal resistance of the batteries and the diffusional resistance ofthe electrical system 66.

With the proceeding in mind, FIGS. 10A-10D describe the illustrativevoltage of the passive battery system 52 in relation to the hypotheticalvehicle operation described above. FIGS. 10A-10D are XY plots that eachincludes a voltage curve that describes the voltage of the passivebattery system between time 0 and time 8, in which voltage is on theY-axis and time is on the X-axis. More specifically, FIG. 10A describesa passive battery system 52 with a non-voltage matched battery pairing,FIG. 10B describes a passive battery system 52 with a first embodimentof a partial voltage matched battery pairing, FIG. 10C describes apassive battery system 52 with a second embodiment of a partial voltagematched battery pairing, and FIG. 10D describes a passive battery system52 with a voltage matched battery pairing. As depicted, FIGS. 10A-10Deach depicts a battery system voltage curve. As used herein, the“battery system voltage” is intended to describe the dynamic voltagemeasured at the terminals of the battery module. Since both thelead-acid battery 30 and the second battery 32 are directly connected tothe bus 68, the voltage across the battery system, the lead-acid battery30, and the second battery 32 is generally the same.

Passive Architecture—Non-Voltage Matched

As described above, FIG. 10A describes a passive battery system when thebatteries 30 and 32 are non-voltage matched. FIG. 10A depicts a voltagecurve 92 that describes the voltage of the passive battery system 52.More specifically, the voltage curve 92 is based on the voltagecharacteristics described in FIG. 5. In other words, a lead-acid battery30 and a NMC battery 32, for example. Additionally, as discussed above,the operation (e.g., charging and discharging) of the passive batterysystem 52 may be controlled via current steering. Furthermore, the NMCbattery 32 may have a higher coulombic efficiency and/or higher chargepower acceptance than the lead-acid battery 30. Accordingly, to moreefficiently capture electrical power generated via regenerative braking,the lead-acid battery 30 may generally be operated between 95-100% stateof charge and the NMC battery 32 may generally be operated at 0% stateof charge. In other words, the lead-acid battery 30 is maintained at arelatively full state of charge to steer the generated electrical powerto the NMC battery 32, and the NMC battery 32 is maintained at arelatively empty state of charge to utilize the full storage capacity(i.e., 0-100% state of charge) of the second battery 32.

Accordingly, during key-off 94 (e.g., between time 0 and time 1), theNMC second battery 32 may be at 0% state of charge. Thus, the lead-acidbattery 30 may supply electrical power to components of the electricalsystem 66 that are powered while the vehicle is key-off 94, such as thealarm system and the engine control unit. As depicted, the batterysystem voltage 92 may decrease as the lead-acid battery state of chargedecreases. At cold crank 96 (e.g., at time 1), the battery systemvoltage 92 sharply decreases as the lead-acid battery 30 supplies powerto the starter 62. As the vehicle begins to accelerate 98 and cruise100, the battery system voltage 92 micro-cycles as the alternator 64periodically turns on to recharge the lead-acid battery 30. Morespecifically, the alternator 64 may be turned on to charge the lead-acidbattery 30 to an upper threshold (e.g., 100% state of charge). Once thelead-acid battery 30 reaches the upper threshold, the alternator 64 maybe turned off and the lead-acid battery 30 may continue supplying powerto the vehicle's electrical system 66 until its state of charge reachesa lower threshold (e.g., 95% state of charge). Once the lead-acidbattery 30 reaches the lower threshold, the alternator 64 may again beturned on to charge the lead-acid battery 30. In the present embodiment,the lead-acid battery 30 may be micro-cycled between 95-100% state ofcharge.

As the vehicle 10 decelerates and generates electrical power viaregenerative braking 102 (e.g., between time 3 and time 4), thealternator 64 outputs electrical power to charge the NMC battery 32. Asdescribed above, because the lead-acid battery 30 may have a highinternal resistance due to its high state of charge, the electricalpower generated may be steered toward the NMC second battery 32, whichmay more efficiently capture the regenerative electrical power due toits higher coulombic efficiency and/or higher charge power acceptancerate. Accordingly, as depicted, the battery system voltage 92 begins toincrease as the NMC battery 32 state of charge increases.

Once the vehicle 10 begins to cruise 104 (e.g., between time 4 and time5), the NMC second battery 32 may supply electrical power to thevehicle's electrical system 66. Accordingly, as depicted, the batterysystem voltage 92 begins to decrease as the NMC battery state of chargedecreases. More specifically, because the NMC battery voltage (e.g.,between 13.3-16.6 volts) is higher than the lead-acid battery voltage(e.g., 11.2-12.9 volts), current generally does not flow out of thelead-acid battery 30 until the NMC battery 32 nears depletion. In otherwords, in some embodiments, the NMC battery 32 may supply electricalpower to the electrical system 66 by itself until nearly depleted, atwhich point, the lead-acid battery 30 may also begin supplyingelectrical power. As described above, the NMC battery state of charge atwhich the lead-acid battery 30 begins to discharge may depend on theinternal resistance of the NMC battery 32 as it discharges and/ordiffusional resistance of the electrical system 66. After cruising 104,the vehicle 10 again decelerates 106 and captures electrical power viaregenerative braking (e.g., between time 5 and time 6). Accordingly, asdepicted, the battery system voltage 92 increases as the NMC batterystate of charge increases.

As the vehicle idles and enters auto-stop 108 (e.g., between time 6 andtime 7), the NMC battery 32 again supplies electrical power to theelectrical system 66 and the battery system voltage 92 decreases as theNMC battery state of charge decreases. In the depicted embodiment, whenthe internal combustion engine 18 is to be warm cranked 110 (e.g., attime 7), the NMC battery 32 still has approximately a 60% state ofcharge (e.g., 14.8 volts). Accordingly, the second battery 32 and thelead-acid battery 30 may both supply power to the starter 62 to restart(e.g., warm crank) the internal combustion engine 18. As depicted, thebattery system voltage 92 again sharply drops to warm crank the internalcombustion engine 18. As described above, the voltage drop at the warmcrank 110 may be less than the voltage drop at the cold crank 96. Afterthe internal combustion engine 18 is restarted, the NMC battery 32 maycontinue supplying power to the vehicle's electrical system 66 by itselfuntil nearly depleted, for example as the vehicle accelerates 112 (e.g.,between time 7 and time 8). In the depicted embodiment, once the NMCbattery 32 is nearly depleted, the lead-acid battery 30 resumessupplying power 114. Supplying power from the second battery 32 untildepleted (e.g., 0% state of charge) enables the second battery 32 tomaximize the use of its storage capacity for capturing regenerativepower. Accordingly, in some embodiments, it may be beneficial to depletethe NMC battery 32 before the lead-acid battery 30 begins to supplypower.

Passive Architecture—First Embodiment Partial Voltage Matched

As described above, FIG. 10B describes a passive battery system when thebatteries 30 and 32 are partial voltage matched, in accordance with afirst embodiment. FIG. 10B depicts a voltage curve 116 that describesthe voltage of a passive battery system 52 when the lead-acid battery 30and the second battery 32 are partial voltage matched, in accordancewith a first embodiment. More specifically, the voltage curve 116 isbased on the voltage characteristics described in FIG. 6. In otherwords, a lead-acid battery 30 and a LTO/NMC battery 32, for example.

As discussed above in regards to the non-voltage match pair, thelead-acid battery 30 may be operated between 95-100% state of charge tosteer regenerative power toward the LTO/NMC battery 32, which may moreefficiently capture regenerative power. Additionally, based on thevoltage characteristics of the batteries 30 and 32 (e.g., currentsteering), the LTO/NMC battery 32 may supply power by itself until itsvoltage nears the lead-acid battery voltage. As used herein, thatvoltage may be referred to as the “threshold voltage.” Accordingly, inthe present embodiment, because the lead-acid battery 30 is operatedbetween 95-100% state of charge, the LTO/NMC battery 32 may supply powerto the electrical system 66 by itself until it nears a voltage thresholdof approximately 12.9 volts, at which point, the lead-acid battery 30 orboth the lead-acid battery 30 and the LTO/NMC battery 32 may supplypower to the electrical system 66. In other words, the lead-acid batterymay begin outputting electrical power once the LTO/NMC battery 32decreases to approximately 20% state of charge. Thus, only a portion ofthe LTO/NMC battery storage capacity is utilized. For example, in thepresent example, 80% (e.g., between 20-100% state of charge) of theLTO/NMC battery storage capacity may be utilized. As used herein, the“first embodiment” of a partial voltage match battery system is intendedto describe maintaining the battery 30 (e.g., lead-acid battery)generally at a full state of charge (e.g., 100% state of charge) andmaintaining the second battery 32 at the state of charge correspondingwith the threshold voltage (e.g., 20% state of charge).

In operation, the first embodiment of partial voltage match is similarto the non-voltage match embodiment described above with the exceptionthat the LTO/NMC battery 32 is generally maintained at 20% state ofcharge. In other words, the lead-acid battery 30 is maintained at arelatively full state of charge to steer the generated electrical powerto the LTO/NMC battery 32, and the LTO/NMC battery 32 is maintained atapproximately 20% state of charge to maximize the storage capacity ofthe second battery 32 (e.g., 20-100% state of charge). Accordingly,during key-off 118 (e.g., between time 0 and time 1), both the lead-acidbattery 30 and the LTO/NMC battery 32 may supply power to the electricalcomponents in the vehicle. As depicted, the battery system voltage 116decreases as the lead-acid battery and LTO/NMC battery states of chargedecrease.

At cold crank 120 (e.g., at time 1), both the lead-acid battery 30 andthe LTO/NMC battery 32 may supply power to the starter 62 to start(e.g., crank) the internal combustion engine 18. Similar to thenon-voltage match embodiment, the battery system voltage 116 sharplydrops. However, as depicted, the voltage drop at the non-voltage matchcold crank 96 may be greater than at the first embodiment of the partialvoltage match cold crank 120. The reduction in the voltage drop is aresult of using both the lead-acid battery 30 and the LTO/NMC battery 32to crank the internal combustion engine as compared to just thelead-acid battery 30.

As the vehicle 10 begins to accelerate 122 and cruise 124, the batterysystem voltage 116 begins to micro-cycle. More specifically, thealternator 64 may micro-cycle the lead-acid battery 30, the LTO/NMCbattery 32, or both to maintain the lead-acid battery between 95-100%state of charge and the LTO/NMC battery 32 at approximately 20% state ofcharge. As the vehicle decelerates and generates electrical power viaregenerative braking 126 (e.g., between time 3 and time 4), thealternator 64 outputs electrical power to charge the LTO/NMC battery 32.However, as described above, less than the full storage capacity of theLTO/NMC battery 32 may be utilized to capture regenerative power (e.g.,80% of storage capacity). In other words, the LTO/NMC battery 32 maycapture regenerative power from 20% state of charge to 100% state ofcharge during regenerative braking. Accordingly, as depicted, thebattery system voltage 116 increases as the LTO/NMC battery state ofcharge increase until the LTO/NMC battery 32 reaches 100% state ofcharge. Once the storage capacity of the LTO/NMC battery 32 is full 128,the battery system voltage 116 remains relatively constant.

As the vehicle 10 cruises 130 (e.g., between time 4 and time 5), theL′I′O/NMC battery 32 may supply electrical power to the vehicle'selectrical system until the LTO/NMC battery 32 nears the thresholdvoltage (e.g., approximately 20% state of charge). As described above,the storage capacity of the LTO/NMC battery 32 may be limited (e.g.,between 20-100% state of charge). In other words, assuming the samecapacity, compared to the NMC battery described above in the non-voltagematch embodiment, the LTO/NMC battery 32 may supply less electricalpower. Accordingly, as depicted, the battery system voltage 116decreases as the LTO/NMC battery state of charge decreases until theLTO/NMC battery 32 nears the threshold voltage (e.g., approximately 20%state of charge). As described above, the lead-acid battery 30 may beginto discharge before the LTO/NMC battery 32 reaches threshold voltage.The exact point may depend on the internal resistance of the secondbattery 32 as it discharges and/or diffusional resistance of theelectrical system 66. For example, the lead-acid battery 30 may begin tosupply power when the LTO/NMC battery 32 reaches 40% state of charge.Upon reaching the threshold voltage, the alternator 64 may be turned onperiodically to micro-cycle 132 the battery system (e.g., the lead-acidbattery 30, the LTO/NMC battery 32, or both). In some embodiments, afterthe LTO/NMC battery 32 reaches the threshold voltage, the second battery32 may continue to supply electrical power, but at a reduced level.

The vehicle 10 again decelerates and captures regenerative electricalpower 134 (e.g., between time 5 and time 6) in the LTO/NMC battery 32.The captured electrical power is then used to supply power theelectrical system 66 while the internal combustion engine 18 is disabledduring auto-stop 136 (e.g., between time 6 and time 7). As describedabove in regards to cruising 130, the storage capacity of the LTO/NMCbattery 32 may be restricted to a portion of the LTO/NMC battery's fullstorage capacity. Accordingly, as depicted, the battery system voltage116 decreases as the LTO/NMC battery state of charge decreases until theLTO/NMC battery 32 nears the threshold voltage. However, because theinternal combustion engine 18 is disabled during auto-stop 136, thebattery system is not micro-cycled. Accordingly, at this point, thebattery system voltage 116 decreases as both the lead-acid battery 30and the LTO/NMC battery 32 discharge 138. In other embodiments, theinternal combustion engine 18 may be restarted to micro-cycle thebattery system voltage 116.

To exit auto-stop 136, the LTO/NMC battery 32 and the lead-acid battery30 may, warm crank 140 (e.g., at time 7) the internal combustion engine18. Once the internal combustion engine 18 is restarted, the batterysystem voltage 116 is again micro-cycled by the alternator 64 as thevehicle accelerates 142.

Passive Architecture—Second Embodiment Partial Voltage Matched

Based on the above description of the first embodiment of the passivebattery system 52 with partial voltage matched batteries, the amount ofregenerative power utilized by the LTO/NMC battery 32 may be less thanits full storage capacity. Accordingly, in a second embodiment of apassive battery system 52 with partial voltage matched batteries, thethreshold voltage may be reduced to increase the amount of regenerativepower that may be captured and supplied by the LTO/NMC battery 32. Forexample, the threshold voltage is lowered to approximately 12.6 volts inthe second embodiment described in FIG. 10C, which depicts a batterysystem voltage curve 144. In other words, the lead-acid battery 30 isgenerally maintained at between 80-85% state of charge and the LTO/NMCbattery 32 is generally maintained at 15% state of charge. Accordingly,in the second embodiment, the LTO/NMC battery 32 may utilize 85% of itsstorage capacity (e.g., 15-100% state of charge) to capture regenerativepower, which is a 5% state of charge increase over the first embodiment(e.g., 80%). In other embodiments, the threshold voltage may be loweredby maintaining the lead-acid battery 30 between 50-55%, 55-60%, 60-65%,65-70%, 70-75%, 85-90% state of charge, or any combination thereof. Asused herein, the “second embodiment” of a partial voltage match batterysystem is intended to describe maintaining the battery 30 (e.g.,lead-acid battery) at a generally less than full state of charge (e.g.,between 80-85% state of charge) to lower the threshold voltage.

Similar to the first embodiment of a passive partial voltage matchbattery system, during key-off 146 (e.g., between time 0 and time 1)both the lead-acid battery 30 and the LTO/NMC battery 32 may supplypower to electrical components in the vehicle, and at cold crank 148(e.g., at time 1) both the lead-acid battery 30 and the LTO/NMC battery32 may supply power to the starter 62 to start (i.e., crank) theinternal combustion engine 18. Accordingly, as depicted, the batterysystem voltage 144 begins to decrease as the lead-acid battery andLTO/NMC battery states of charge decrease. However, as described above,the lead-acid battery 30 is generally maintained between 80-85% state ofcharge and the LTO/NMC battery 32 is generally maintained at 15% stateof charge. In other words, assuming the same total capacity, the amountof electrical power stored in the second embodiment may be less that theamount of electrical power stored in the first embodiment (e.g., 95-100%lead-acid battery state of charge and 25% NMC battery state of charge).Accordingly, in some embodiments, to ensure that the battery system hasstored sufficient electrical power to support the electrical componentsduring key-off 146 and to cold crank 148 the internal combustion engine18, a larger capacity battery system (e.g., lead-acid battery 30 andLTO/NMC battery 32) may be utilized. In some embodiments, the storagecapacity of the battery system may be increased to enable the vehicle tocold crank 148 after sitting idle for thirty days.

Again similar to the first embodiment, as the vehicle 10 begins toaccelerate 150 and cruise 152, the vehicle system voltage 144 ismicro-cycled to maintain the lead-acid battery generally between 80-85%state of charge and the LTO/NMC battery 32 at approximately 15% state ofcharge (e.g., target states of charge). More generally, the lead-acidbattery 30 is maintained at a partial state of charge while the LTO/NMCbattery 32 is maintained at its lowest state of charge (e.g.,corresponding with the threshold voltage). As the vehicle deceleratesand generates electrical power via regenerative braking 154 (e.g.,between time 3 and time 4), the alternator 64 outputs electrical powerto charge the battery system.

More specifically, because the lead-acid battery 30 is maintained atless than full state of charge, the current of the regenerative power issplit between the lead-acid battery 30 and the LTO/NMC battery 32, whichas describe above may depend on the internal resistance of each. Inother words, the alternator 64 charges both the lead-acid battery 30 andthe LTO/NMC battery 32. However, as described above, the LTO/NMC battery32 may have a higher coulombic efficiency and/or a higher charge poweracceptance rate than the lead-acid battery 30. Accordingly, since alarger portion of the regenerative power is captured by the lead-acidbattery 30, the regenerative power may be less efficiently captured inthe second embodiment than the first embodiment. Thus, as depicted, thebattery system voltage 144 increases during regenerative braking 154 asthe lead-acid battery and LTO/NMC battery states of charge increase, butthe voltage increase during the regenerative braking 154 in the secondembodiment may be flatter than the voltage increase during theregenerative braking 126 in the first embodiment because the LTO/NMCbattery state of charge increases at a slower rate in the secondembodiment. Accordingly, as depicted, the LTO/NMC battery 32 has notreached its full capacity (e.g., 16 volts) during regenerative braking154 (e.g., charging 155).

As in the first embodiment, when the vehicle 10 cruises 156 (e.g.,between time 4 and time 5), the LTO/NMC battery 32 may supply electricalpower to the vehicle's electrical system 66 until it nears the thresholdvoltage (e.g., approximately 15% state of charge). As described above,the lead-acid battery 30 may begin to discharge before the LTO/NMCbattery 32 reaches threshold voltage depending on the internalresistance of the second battery 32 as it discharges and/or diffusionalresistance of the electrical system 66. In some embodiments, the LTO/NMCbattery 32 may continue to supply electrical power after reaching thethreshold voltage, but at a reduced level. As described above, theamount of regenerative power stored in the LTO/NMC battery 32 may beincreased in the second embodiment. Accordingly, as depicted, the storedpower in the LTO/NMC battery 32 is sufficient to supply power to theelectrical system 66 without turning on the alternator 64. As depicted,the battery system voltage 144 again increases as regenerativeelectrical power is captured in both the lead-acid battery 30 and theLTO/NMC battery 32 during regenerative braking 158 (e.g., between time 5and 6), the battery system voltage 144 decreases as the battery systemsupplies electrical power to the electrical system 66 during auto-stop160 (e.g., between time 6 and time 7), the battery system voltage 144drops sharply as the battery system supplies electrical power to thealternator 64 to warm crank 162 (e.g., at time 7) the internalcombustion engine 18, and the battery system voltage 144 is micro-cycledas the vehicle accelerates 164 (e.g., between time 7 and time 8).

Passive Architecture—Voltage Matched

As described above, FIG. 10D describes a passive battery system when thebatteries 30 and 32 are voltage matched. FIG. 10D depicts a voltagecurve 166 that describes the voltage of the passive battery system 52.More specifically, the voltage curve 166 is based on the voltagecharacteristics described in FIG. 7. In other words, a lead-acid battery30 and a LTO/LMO battery 32, for example. As described above, the secondbattery 32 may supply power to the electrical system 66 by itself untilthe second battery 32 nears the threshold voltage. Accordingly, similarto second embodiment of the partial voltage match described above, thethreshold voltage may be reduced to increase the storage capability ofthe LTO/LMO battery 32. Illustratively, if the threshold voltage isapproximately 12.9 volts, the lead-acid battery 30 is generallymaintained at between 95-100% state of charge and the LTO/LMO battery 32is maintained at approximately 75% state of charge. In other words, theLTO/LMO battery 32 is capable of utilizing 25% of its storage capacityto capture regenerative power (e.g., 75-100% state of charge).Comparatively, if the threshold voltage is reduced to approximately 12.3volts, the lead-acid battery 30 is generally maintained at between60-65% state of charge (e.g., generally less than full state of charge)and the LTO/LMO battery 32 is generally maintained at 35% state ofcharge. Accordingly, the LTO/LMO battery is capable of utilizing 65% ofits storage capacity to capture regenerative power (e.g., 35-100% stateof charge).

In operation, the voltage match embodiment may function similarly to thesecond embodiment of the partial voltage match embodiment. Duringkey-off 168 (e.g., between time 0 and time 1) both the lead-acid battery30 and the LTO/LMO battery 32 may supply power to electrical componentsin the vehicle, and at cold crank 170 (e.g., at time 1) both thelead-acid battery 30 and the LTO/LMO battery 32 may supply power to thestarter 62 to start (e.g., crank) the internal combustion engine 18.Accordingly, as depicted, the battery system voltage 166 begins todecrease as the lead-acid battery and LTO/NMC battery states of chargedecrease. However, similar to the second embodiment of the partialvoltage match, reducing the threshold voltage also reduces the amount ofelectrical power stored in the battery system (e.g., 60-65% lead-acidstate of charge and 35% LTO/LMO battery state of charge). Accordingly,the storage capacity of the battery system may be increased even furtherto enable the vehicle to cold crank 170 after sitting idle for thirtydays.

Similar to the embodiments described above, the battery system voltage166 is micro-cycled as the vehicle 10 accelerates 172 and cruises 174.More specifically, the lead-acid battery 30 may be generally maintainedbetween 60-65% state of charge and the LTO/LMO battery 32 may bemaintained at approximately 35% state of charge (e.g., target states ofcharge). As the vehicle 10 decelerates and generates electrical powervia regenerative braking 176 (e.g., between time 3 and time 4), thealternator 64 outputs electrical power to charge both the lead-acidbattery 30 and the LTO/LMO battery 32 because the lead-acid battery 30is maintained at less than full state of charge. Accordingly, asdepicted, the battery system voltage 166 increases as the lead-acidbattery and LTO/LMO battery states of charge increase. However, asdescribed above, the LTO/LMO battery 32 may have a higher coulombicefficiency and/or a higher charge power acceptance rate than thelead-acid battery 30, which may result in the regenerative power beingless efficiently captured in the lead-acid battery 30.

Furthermore, when the vehicle 10 begins to cruise 178 (e.g., betweentime 4 and time 5), the LTO/LMO battery 32 may supply electrical powerto the vehicle's electrical system 66 until it nears the thresholdvoltage (e.g., approximately 35% state of charge). As described above,the lead-acid battery 30 may begin to discharge before the LTO/NMCbattery 32 reaches threshold voltage depending on the internalresistance of the second battery 32 as it discharges and/or diffusionalresistance of the electrical system 66. Upon reaching the thresholdvoltage, the alternator 64 may periodically micro-cycle the batterysystem voltage 166. Additionally, as depicted, the battery systemvoltage 166 increases as regenerative electrical power is captured inboth the lead-acid battery 30 and the LTO/LMO battery 32 duringregenerative braking 180 (e.g., between time 5 and 6), the batterysystem voltage 166 decreases as the battery system supplies electricalpower to the electrical system 66 during auto-stop 182 (e.g., betweentime 6 and time 7). In some embodiments, both the lead-acid battery 30and the LTO/LMO battery 32 may supply power during auto-stop 182.Furthermore, in other embodiments, the alternator may be restarted tomaintain the battery system voltage 166 above the threshold voltage. Thebattery system voltage 166 then drops sharply as the battery systemsupplies electrical power to the alternator 64 to warm crank 184 (e.g.,at time 7) the internal combustion engine 18, and the battery systemvoltage 144 is micro-cycled as the vehicle accelerates 186 (e.g.,between time 7 and time 8).

Based on the various embodiments of passive battery systems 52 describedabove, the control algorithm utilized by the battery control unit 34 maybe less complex than the algorithm utilized for other architectures.More specifically, based on the voltage characteristics of the batteries(e.g., non-voltage matched, partial voltage matched, or voltage matched)the battery control unit 34 may control the operation of the passivebattery system 52 by turning on/off the alternator 64 to maintain eachof the batteries 30 and 32 at their respective target states of charge.For example, in a non-voltage matched embodiment, the battery controlunit 34 may generally maintain the lead-acid battery 30 at a full stateof charge to steer regenerative power to the second battery 32, and maygenerally maintain the second battery 32 at a generally empty state ofcharge to more fully utilize the storage capacity of the second battery32. Additionally, in a voltage matched or partial voltage matchedembodiment, the battery control unit 34 may generally maintain thelead-acid battery 30 at less than a full state of charge to reduce thethreshold voltage and increase the utilization of the second batterystorage capacity.

Semi-Passive Architectures for Dual Chemistry Batteries

To increase the control over the operation of one of the batteries 30 or32, a semi-passive architecture 54, as depicted in FIGS. 11A and B, maybe utilized. More specifically, a semi-passive architecture 54 enablesone of the batteries 30 or 32 to be selectively connected anddisconnected from the bus 68. For example, FIG. 11A, depicts anembodiment of a semi-passive architecture 54A with a switch 188Aincluded between the lead-acid battery 30 and the bus 68 while thesecond battery 32 is directly connected to the bus 68. As used herein, a“switch” is intended to describe any mechanism that can selectivelyconnect and disconnect a battery, such as a hardware switch, acontactor, or a relay. In some embodiments, it may be desirable toutilize a relay to minimize the risk of arcing, which may result fromthe use of a hardware switch.

Alternatively, FIG. 11B depicts an embodiment of a semi-passivearchitecture 54B with a switch 188B included between the second battery32 and the bus 68 while the lead-acid battery 30 is directly connectedto the bus 68. In operation, the switch 188B may be closed when it isdesirable to charge or discharge the second battery 32. On the otherhand, the switch 188B may be open when the second battery 32 is neithercharging nor discharging. In other words, current steeringcharacteristics may control the operation of the lead-acid battery 30while the battery control unit 34 may control the operation of thesecond battery 32 directly via the switch 188B.

Accordingly, in operation, the semi-passive battery system 54embodiments may be similar to the passive battery system 52 embodiments.However, as will be described in further detail below, the semi-passivebattery system architecture 54B may improve the reliability of thebattery system by enabling the second battery 32 to be disabled (e.g.,disconnected from the vehicle 10) when it is undesirable to chargeand/or discharge the second battery 32. Additionally, the semi-passivebattery system 54A may improve reliability of the battery system byenabling the lead-acid battery 30 to be disabled (e.g., disconnectedfrom the vehicle 10) when it is undesirable to charge and/or dischargethe lead-acid battery 30, for example to protect the lead-acid battery30 from overvoltage. In other words, operation of one of the batteries30 or 32 may be directly controlled by the battery control unit 34.

With the proceeding in mind, FIGS. 12A-12D describe the illustrativevoltage of the semi-passive battery system 54B, depicted in FIG. 11B, inrelation to the hypothetical vehicle operation described above. FIGS.12A-12D are XY plots that each includes a voltage curve that describesthe dynamic voltage of the semi-passive battery system 54B and a secondbattery voltage curve that describes the dynamic voltage of the secondbattery 32 between time 0 and time 8, in which voltage is on the Y-axisand time is on the X-axis. More specifically, FIG. 12A describes asemi-passive battery system 54B with a non-voltage matched batterypairing, FIG. 12B describes a semi-passive battery system 54B with afirst embodiment of a partial voltage matched battery pairing, FIG. 12Cdescribes a semi-passive battery system 54B with a second embodiment ofa partial voltage matched battery pairing, and FIG. 12D describes asemi-passive battery system 54B with a voltage matched battery pairing.As should be appreciated, since the lead-acid battery 30 is directlyconnected to the bus 68, the battery system voltage will be the same asthe lead-acid battery voltage.

Semi-Passive Architecture—Non-Voltage Matched

Functionally, the semi-passive embodiments (e.g., non-voltage match,first embodiment partial voltage match, second embodiment partialvoltage match, voltage match) are similar to their respective passivebattery system embodiments. For example, the semi-passive non-voltagematch battery system described in FIG. 12A is generally the same as thepassive non-voltage match battery system described in FIG. 10A. Asdescribed above, FIG. 12A depicts a battery system voltage curve 190 anda second battery voltage curve 192 when the lead-acid battery 30 and thesecond battery 32 are non-voltage matched. More specifically, thevoltage curves 190 and 192 are based on the voltage characteristicsdescribed in FIG. 5. In other words, a lead-acid battery 30 and a NMCbattery 32.

Similar to the battery system voltage 92 described in FIG. 10A, thebattery system voltage 190 decreases as the lead-acid battery supplieselectrical power to the component of the electrical system 66 duringkey-off 194 (e.g., between time 0 and time 1), sharply drops as thelead-acid battery 30 cold cranks 196 the internal combustion engine(e.g., at time 1), micro-cycles while the vehicle accelerates 198 andcruises 200 (e.g., between time 1 and time 3), increases as electricalpower is stored in the NMC battery 32 during regenerative braking 202(e.g., between time 3 and time 4), decreases as the NMC battery 32supplies electrical power to the electrical system 66 during cruising204 (e.g., between time 4 and time 5), increases as electrical power isagain stored in the NMC battery 32 during regenerative braking 206(e.g., between time 5 and time 6), decreases as the NMC battery 32supplies electrical power to the electrical system 66 during auto-stop208 (e.g., between time 6 and time 7), sharply drops to warm crank 210the internal combustion engine 18 (e.g., at time 7), decreases until theelectrical power stored in the NMC battery 32 is depleted 212 or nearlydepleted, and micro-cycles thereafter (e.g., micro-cycling).

More specifically, as described above, the switch 188B may be closedwhen it is desirable to charge or discharge the second battery 32. Forexample, between time 0 and time 3 (e.g., key-off 194, cold crank 196,acceleration 198, and cruising 200), the switch 188B may be open toenable the lead-acid battery 30 to supply electrical power to theelectrical system 66 by itself. Accordingly, as depicted, the NMCbattery voltage 192 is maintained at approximately 113 volts (e.g., 0%state of charge). Additionally, between time 3 and time 7 (e.g.,regenerative braking 202, cruising 204, regenerative braking 206,auto-stop 208, and warm-crank 210), the switch 188B may be closed toenable the NMC battery 32 to charge, for example during regenerativebraking 202 and 206, and discharge for example during cruising 204 andauto-stop 208. Furthermore, the switch 188B may remain closed until theelectrical power stored in the NMC battery 32 is depleted 212.Accordingly, since the NMC battery 32 contains approximately 60% stateof charge, the lead-acid battery 30 along with the NMC battery 32 mayboth supply power to warm crank 210 the internal combustion engine asdepicted. More specifically, whether to utilize the second battery 32 tocrank the internal combustion engine may be based at least in part on aminimum state of charge for the second battery. In some embodiments, theminimum state of charge may be 20%, 40%, or 60% of second battery stateof charge. As used herein, “minimum state of charge” is intended todescribe the minimum amount of power, which is a function of the batterystate of charge, that may be contributed by the second battery 32 tofacilitate a vehicle operation, such as crank the internal combustionengine 18 or supply power to the electrical system 66. Once the NMCbattery 32 is depleted, the switch 188B may be open, disconnecting theNMC battery 32 and enabling the lead-acid battery 30 may supply power tothe electrical system 66 by itself.

Semi-Passive Architecture—First Embodiment Partial Voltage Matched

As described above, FIG. 12B describes a semi-passive battery system 54Bwhen the batteries 30 and 32 are partial voltage matched, in accordancewith the first embodiment. FIG. 12B depicts a battery system voltagecurve 214 and a second battery voltage curve 216, in accordance with thefirst embodiment. More specifically, the voltage curves 214 and 216 arebased on the voltage characteristics described in FIG. 6. In otherwords, a lead-acid battery 30 and a LTO/NMC battery 32.

Similar to the battery system voltage 116 described in FIG. 10B, thebattery system voltage 214 decreases as the lead-acid battery 30supplies electrical power to the electrical system. 66 during key-off218 (e.g., between time 0 and time 1), sharply drops as the lead-acidbattery 30 cold cranks 220 the internal combustion engine (e.g., at time1), micro-cycles (e.g., to maintain the lead-acid battery 30 between95-100% state of charge) while the vehicle accelerates 222 and cruises224 (e.g., between time 1 and time 3), increases as electrical power isstored in the LTO/NMC battery 32 during regenerative braking 226 (e.g.,between time 3 and time 4), decreases as the battery system supplieselectrical power to the electrical system 66 during cruising 228 (e.g.,between time 4 and time 5), increases as electrical power is againstored in the LTO/NMC battery 32 during regenerative braking 230 (e.g.,between time 5 and time 6), decreases as the battery system supplieselectrical power to the electrical system 66 during auto-stop 232 (e.g.,between time 6 and time 7), sharply drops as the lead-acid battery 30warm cranks 234 the internal combustion engine 18 (e.g., at time 7), andmicro-cycles after the electrical power stored in the LTO/NMC battery 32is depleted or nearly depleted (e.g., during acceleration 236).

More specifically, similar to the semi-passive non-voltage matchdescribed above, in the depicted embodiment, the switch 188B is openbetween time 0 and time 3 (e.g., key-off 218, cold crank 220,acceleration 222, and cruising 224) to enable the lead-acid battery 30to supply power to the electrical system 66 by itself. Additionally, theswitch 188B may open after the LTO/NMC battery 32 has discharged to thethreshold voltage. For example, in the depicted embodiment, the switch188B is open during micro-cycling 235 and discharging 237 to disconnectthe LTO/NMC battery 32. Accordingly, as depicted, the LTO/NMC batteryvoltage 216 remains relatively constant during these periods. As can beappreciated, the LTO/NMC battery voltage 216 may experience some decaydue to voltage relaxation and/or self-discharge. Furthermore, in thedepicted embodiment, since the switch 188B is open, the lead-acidbattery 30 supplies power to warm crank 234 the internal combustionengine 18 by itself.

On the other hand, the switch 188B may be closed to enable the LTO/NMCbattery to charge/discharge. For example, in the depicted embodiment,the switch 188B is closed during regenerative braking 226 and 230 tocharge the LTO/NMC battery 32. Additionally, the switch 188B is closedwhile the LTO/NMC battery 32 supplies power, for example during theportion of cruising 228 and auto-stop 232 before reaching its thresholdvoltage (e.g., before micro-cycling 235 and discharging 237). Moregenerally, the switch 188B may be closed when electrical power isdesired by the electrical system 66 and the second battery 32 is above aminimum state of charge.

Semi-Passive Architecture—Second Embodiment Partial Voltage Matched

Additionally, as described above, FIG. 12C describes a semi-passivebattery system 54B when the batteries 30 and 32 are partial voltagematched, in accordance with the second embodiment. FIG. 12C depicts abattery system voltage curve 238 that describes the voltage of thebattery system and a second battery voltage curve 240 that describes thevoltage of a second battery 32. More specifically, the voltage curves238 and 240 are based on the voltage characteristics described in FIG.6. In other words, a lead-acid battery 30 and a LTO/NMC battery 32.

Similar to the battery system voltage 144 described in FIG. 10C, thebattery system voltage 238 decreases as the lead-acid battery 30supplies electrical power to the component of the electrical system 66during key-off 246 (e.g., between time 0 and time 1), sharply drops asthe lead-acid battery 30 cold cranks 248 the internal combustion engine(e.g., at time 1), micro-cycles (e.g., to maintain the lead-acid batterybetween 80-85% state of charge) while the vehicle accelerates 250 andcruises 252 (e.g., between time 1 and time 3), increases as electricalpower is stored in the LTO/NMC battery 32 during regenerative braking254 (e.g., between time 3 and time 4), decreases as the LTO/NMC battery32 supplies electrical power to the electrical system 66 during cruising256 (e.g., between time 4 and time 5), increases as electrical power isagain stored in the LTO/NMC battery 32 during regenerative braking 258(e.g., between time 5 and time 6), decreases as the LTO/NMC battery 32supplies electrical power to the electrical system 66 during auto-stop232 (e.g., between time 6 and time 7), sharply drops to warm crank 262the internal combustion engine 18 (e.g., at time 7), and micro-cyclesafter the electrical power stored in the LTO/NMC battery 32 is depletedor nearly depleted (e.g., during acceleration 264).

More specifically, similar to the first semi-passive partial voltagematch embodiment described above, in the depicted embodiment, the switch188B is open between time 0 and time 3 (e.g., key-off 246, cold crank248, acceleration 250, and cruising 252) to enable the lead-acid battery30 to supply power to the electrical system 66 by itself. Additionally,the switch 188B may open after the LTO/NMC battery 32 has discharged tothe threshold voltage. For example, in the depicted embodiment, theswitch 188B opens to disconnect the LTO/NMC battery 32 and the lead-acidbattery 30 provides power (e.g., during micro-cycling 265). Accordingly,as depicted, the LTO/NMC battery voltage 240 remains at a relativelyconstant voltage during these periods. Furthermore, since the LTO/NMCbattery 32 has not reached the threshold voltage, the LTO/NMC battery 32along with the lead-acid battery 30 may both supply power to warm crank262 the internal combustion engine 18.

On the other hand, the switch 188B may be closed to enable the LTO/NMCbattery to charge/discharge. For example, in the depicted embodiment,the switch 188B is closed during regenerative braking 254 and 258 tocharge the LTO/NMC battery 32. Additionally, the switch 188B is closedwhile the LTO/NMC battery 32 supplies power, for example during cruising256 and auto-stop 260.

Semi-Passive Architecture—Voltage Matched

Furthermore, as described above, FIG. 12D describes a semi-passivebattery system 54B when the batteries 30 and 32 are voltage matched. Asdepicted, FIG. 12D depicts a battery system voltage curve 242 thatdescribes the voltage of the battery system and a second battery voltagecurve 244 that describes the voltage of a second battery 32. Morespecifically, the voltage curves 242 and 244 are based on the voltagecharacteristics described in FIG. 7. In other words, a lead-acid battery30 and a LTO/LMO battery 32.

Similar to the battery system voltage 166 described in FIG. 10D, thebattery system voltage 242 decreases as the lead-acid battery 30supplies electrical power to the component of the electrical system 66during key-off 266 (e.g., between time 0 and time 1), sharply drops asthe lead-acid battery 30 cold cranks 268 the internal combustion engine(e.g., at time 1), micro-cycles (e.g., to maintain the lead-acid batterybetween 60-65% state of charge) while the vehicle accelerates 270 andcruises 272 (e.g., between time 1 and time 3), increases as electricalpower is stored in the LTO/LMO battery 32 during regenerative braking274 (e.g., between time 3 and time 4), decreases as the battery systemsupplies electrical power to the electrical system 66 during cruising276 (e.g., between time 4 and time 5), increases as electrical power isagain stored in the LTO/LMO battery 32 during regenerative braking 278(e.g., between time 5 and time 6), decreases as the battery systemsupplies electrical power to the electrical system 66 during auto-stop280 (e.g., between time 6 and time 7), sharply drops as the lead-acidbattery warm cranks 282 the internal combustion engine 18 (e.g., at time7), and micro-cycles after the electrical power stored in the LTO/LMObattery 32 is depleted or nearly depleted (e.g., during acceleration284).

More specifically, similar to the semi-passive embodiments describedabove, in the depicted embodiment, the switch 188B is open between time0 and time 3 (e.g., key-off 266, cold crank 268, acceleration 270, andcruising 272) to enable the lead-acid battery 30 to supply power to theelectrical system 66 by itself. Additionally, the switch 188B may openafter the LTO/LMO battery 32 has discharged to the threshold voltage.For example, in the depicted embodiment, when the threshold voltage isreached, the switch 188B opens to disconnect the NMC battery 32 duringmicro-cycling 283 or discharging 285. Accordingly, as depicted, theLTO/NMC battery voltage 240 remains at a relatively constant voltageduring these periods. Furthermore, in the depicted embodiment, since theswitch 188B is open, the lead-acid battery 30 supplies power to warmcrank 282 the internal combustion engine 18 by itself.

On the other hand, the switch 188E may be closed to enable the LTO/NMCbattery to charge/discharge. For example, in the depicted embodiment,the switch 188B is closed during regenerative braking 274 and 278 tocharge the LTO/LMO battery 32. Additionally, the switch 188E is closedwhile the LTO/LMO battery 32 supplies power, for example during theportion of cruising 276 and auto-stop 280 before reaching its thresholdvoltage (e.g., before micro-cycling 283 and discharging 285).

As discussed above with regard to the embodiments described in FIGS.12A-12D, the switch 188B may be open to disconnect the second battery 32when it is undesirable to charge or discharge the second battery 32. Forexample, the switch 188B may be open when the lead-acid battery 30 issupplying power (e.g., during key-off, cold crank, acceleration, andcruising). Additionally, the switch 188B may be open when the secondbattery 32 discharges to the threshold voltage (e.g., 235, 237, 265,283, or 285). Comparatively, as discussed above with regard to thepassive embodiments described in FIGS. 10A-10D, the lead-acid battery 30along with the second battery 32 may supply power during key-off (e.g.,118, 146, or 168), and the alternator 64 may micro-cycle both thelead-acid battery 30 and the second battery 32 because the secondbattery 32 is directly coupled to the bus 68.

In some embodiments, micro-cycling the lead-acid battery 30 by itself(e.g., without micro-cycling the second battery 32) may increase thevehicle's fuel economy and/or reduce undesirable emissions because thealternator 64 charges a single battery (e.g., lead-acid battery 30) ascompared to two batteries (e.g., lead-acid battery 30 and second battery32). Additionally, not micro-cycling the second battery 32 may improvethe lifespan of the second battery 32 because the second battery 32 isnot repeatedly charged and discharged during micro-cycling. Accordingly,the overall cost of a semi-passive battery system 54B may be reducedbased on these factors.

Similarly, including the switch 188A to selectively couple the lead-acidbattery 30, as depicted in FIG. 11A, may improve the lifespan of thelead-acid battery 30 and improve the recharge efficiency of the secondbattery 32. For example, when the lead-acid battery 30 is maintained atless than full state of charge (e.g., the second partial voltage matchembodiment) the switch 188A may disconnect the lead-acid battery 30during regenerative braking to steer all of the regenerative power tothe second battery 32, which more efficiently captures the regenerativepower. Additionally, the switch 188A may disconnect the lead-acidbattery 30 to enable the second battery 32 to be charged at a highervoltage (e.g., 16.8 volts), which may be higher than the maximumcharging voltage of to the lead-acid battery 30 (e.g., overvoltage), toimprove the charging rate of the second battery 32. For example, in thepresent embodiment, the alternator 64 may output a voltage up to 16.8volts to charge the NMC battery 32. However, the maximum chargingvoltage of lead-acid battery 30 may be 14.8 volts because above thatpoint the lead-acid battery 30 may begin to produce oxygen and hydrogengas, which negatively affects the lifespan of the lead-acid battery 30.In other words, the switch 188A may be opened to enable the secondbattery 32 to be more optimally charged while protecting the lead-acidbattery 30 from overvoltage, for example when the batteries 30 and 32are non-voltage matched or partial voltage matched.

Based on the various embodiments of semi-passive battery systems 54described above, the control algorithm utilized by the battery controlunit 34 may be more complex than the algorithm utilized for passivebattery systems 52. More specifically, in addition to controlling thealternator 64, the battery control unit 34 may close and open the switch188 to control the operation of the semi-passive battery system 54. Asdescribed above, the switch 188 may be closed when the battery 30 or 32is charging or discharging and open otherwise. For example, in someembodiments, the battery control unit 34 may open the switch 188A toenable the second battery 32 to be more optimally charged (e.g., with ahigher charging voltage) while protecting the lead-acid battery 30 fromovervoltage. Accordingly, the battery control unit 34 may turn on/offthe alternator 64 as well as open/close the switch 188 to maintain eachof the batteries 30 and 32 at their respective target states of charge.In addition to opening/closing the switch 188 to facilitate maintainingthe batteries 30 and 32 at their target states of charge, the batterycontrol unit 34 may disconnect the battery 30 or 32 for other reasons,such as extreme temperatures that may cause one of the batteries 30 or32 to be outside of its optimum operating zones.

Switch Passive Architectures for Dual Chemistry Batteries

Further expanding on the control provided by the semi-passivearchitecture to both batteries 30 and 32, a switch passive architecture56, as depicted in FIG. 13, may be utilized. Similar to the semi-passivearchitecture 54 described above, switches may be utilized to selectivelyconnect a battery 30 or 32 to the bus 68. For example, as depicted inFIG. 13, a first switch 286 is included between the lead-acid battery 30and the bus 68, and a second switch 288 is included between the secondbattery 32 and the bus 68. Accordingly, the switch-passive architecture56 provides greater control over the operation of both batteries 30 and32 by enabling each battery 30 and 32 to be selectively connected anddisconnected from the bus 68. For example, in some embodiments, thisenables the lead-acid battery 30 to be disconnected while the secondbattery 32 is charging/discharging, and vice versa. In other words, thebattery control unit 34 may control the operation of the lead-acidbattery 30 via the first switch 286 and the operation of the secondbattery 32 via the second switch 288, which enables the lead-acidbattery 30 and the second battery 32 to operate (e.g., charge ordischarge) relatively independently.

With the proceeding in mind, FIGS. 14A-14D describe the illustrativevoltage of the switch passive battery system 56 in relation to thehypothetical vehicle operation described above. FIGS. 14A-14D are XYplots that each includes a battery system voltage curve that describesthe dynamic voltage of the switch passive battery system 56, a lead-acidbattery voltage curve that describes the dynamic voltage of thelead-acid battery 30, and a second battery voltage curve that describesthe dynamic voltage of the second battery 32 between time 0 and time 8,in which voltage is on the Y-axis and time is on the X-axis. Morespecifically, FIG. 14A describes a switch passive battery system 56 witha non-voltage matched battery pairing, FIG. 14B describes a switchpassive battery system 56 with the first embodiment of a partial voltagematched battery pairing, FIG. 14C describes a switch passive batterysystem 56 with a third embodiment of a partial voltage matched batterypairing, and FIG. 14D describes a switch passive battery system 56 witha voltage matched battery pairing. As will be illustrated in theembodiments described below, the battery system voltage follows thelead-acid battery voltage, the second battery voltage, or both dependingon the position (e.g., open or closed) of the switches 286 and 288.

Switch Passive—Non-Voltage Matched

Functionally, the switch passive embodiments (e.g., non-voltage match,first embodiment partial voltage match, second embodiment partialvoltage match, voltage match) are similar to their respectivesemi-passive battery system embodiments. For example, FIG. 14A depicts abattery system voltage curve 290 (represented as dotted line), alead-acid battery curve 292, and a second battery curve 294 when thelead-acid battery 30 and the second battery 32 are non-voltage matched.More specifically, the voltage curves 290, 292, and 294 are based on thevoltage characteristics described in FIG. 5. In other words, a lead-acidbattery 30 and a NMC battery 32.

Similar to the battery system voltage 190 described in FIG. 12A, thebattery system voltage 290 decreases as the lead-acid battery 30supplies electrical power to the electrical system 66 during key-off 296(e.g., between time 0 and time 1), sharply drops as the lead-acidbattery 30 cold cranks 298 the internal combustion engine (e.g., at time1), micro-cycles (e.g., to maintain the lead-acid battery 30 between95-100% state of charge) while the vehicle accelerates 300 and cruises302 (e.g., between time 1 and time 3), increases as electrical power isstored in the NMC battery 32 during regenerative braking 304 (e.g.,between time 3 and time 4), decreases as the NMC battery 32 supplieselectrical power to the electrical system 66 during cruising 306 (e.g.,between time 4 and time 5), increases as electrical power is againstored in the NMC battery 32 during regenerative braking 308 (e.g.,between time 5 and time 6), decreases as the NMC battery 32 supplieselectrical power to the electrical system 66 during auto-stop 310 (e.g.,between time 6 and time 7), sharply drops as the NMC battery 32 warmcranks 312 the internal combustion engine 18 (e.g., at time 7),decreases until the electrical power stored in the NMC battery 32 isdepleted 314 or nearly depleted, and micro-cycles thereafter (e.g.,after 316).

More specifically, as described above, the first switch 286 may beclosed while the lead-acid battery 30 supplies power, and the secondswitch 288 may be closed when it is desirable to charge or discharge thesecond battery 32. For example, in the depicted embodiment, the firstswitch 286 is closed and the second switch 288 is open between time 0and time 3 (e.g., key-off 296, cold crank 298, acceleration 300, andcruising 302) to enable the lead-acid battery 30 to supply electricalpower to the electrical system 66 by itself. Accordingly, as depicted,the battery system voltage 290 is the lead-acid battery voltage 292 andthe NMC battery voltage 294 is maintained at approximately 13.3 volts(e.g., 0% state of charge).

Between time 3 and time 7 (e.g., regenerative braking 304, cruising 306,regenerative braking 308, and auto-stop 310), the first switch 286 isopen and the second switch 288 is closed to enable the NMC battery 32 tocharge, for example during regenerative braking 304 and 308, anddischarge, for example during cruising 306 and auto-stop 310.Accordingly, as depicted, the battery system voltage 290 is the secondbattery voltage 294 while the NMC battery 32 captures regenerative powerand supplies power to the electrical system 66 by itself, and thelead-acid voltage 292 is maintained at approximately 12.9 volts (e.g.,100% state of charge).

Similar to the semi-passive battery system 54A, the first switch 286 maybe open to enable the second battery 32 to be more efficiently chargedwhile protecting the lead-acid battery 30 from overvoltage. For example,in the depicted embodiment to increase the charge power acceptance rateof the NMC battery 32, the alternator 64 may output up to the maximumcharging voltage of the NMC battery 32 (e.g., 16.8 volts). However, themaximum charging voltage may be above the maximum charging voltage ofthe lead-acid battery 30 (e.g., overvoltage), which may reduce thelifespan of the lead-acid battery 30 (e.g., by producing oxygen andhydrogen gas). In other words, the first switch 286 may open to protectthe lead-acid battery 30.

The second switch 288 may remain closed until the electrical powerstored in the NMC battery 32 is nearly depleted or until the electricalpower output by the NMC battery is lower than the electrical powerdesired by the electrical system 66, at which point, the second switch288 may open and the first switch 286 may close to enable the lead-acidbattery 30 may supply power to the electrical system 66 (e.g., atmicro-cycling 318). In other embodiments, both the first switch 286 andthe second switch 288 may both be closed to further deplete the NMCbattery 32. Accordingly, as depicted, since not yet depleted, the NMCbattery 32 may supply power to warm crank 312 the internal combustionengine by itself. Thus, in the present embodiment, the capturedregenerative power may be used in place of the power stored in thelead-acid battery.

Switch Passive—First Embodiment Partial Voltage Matched

As described above, FIG. 14B describes a switch passive battery systemwhen the batteries 30 and 32 are partial voltage matched, in accordancewith the first embodiment. FIG. 14B depicts a battery system voltagecurve 320 (represented by dotted line), a lead-acid battery voltagecurve 322, and a second battery voltage curve 324. More specifically,the voltage curves 322 and 324 are based on the voltage characteristicsdescribed in FIG. 6. In other words, a lead-acid battery 30 and aLTO/NMC battery 32.

Similar to the battery system voltage 214 described in FIG. 12B, thebattery system voltage 320 decreases as the lead-acid battery 30supplies electrical power to the electrical system 66 during key-off 326(e.g., between time 0 and time 1), sharply drops as the lead-acidbattery 30 cold cranks 328 the internal combustion engine (e.g., at time1), micro-cycles (e.g., to maintain the lead-acid battery 30 between95-100% state of charge) while the vehicle accelerates 330 and cruises332 (e.g., between time 1 and time 3), increases as electrical power isstored in the LTO/NMC battery 32 during regenerative braking 334 (e.g.,between time 3 and time 4), decreases as the battery system supplieselectrical power to the electrical system 66 during cruising 336 (e.g.,between time 4 and time 5), increases as electrical power is againstored in the LTO/NMC battery 32 during regenerative braking 338 (e.g.,between time 5 and time 6), decreases as the battery system supplieselectrical power to the electrical system 66 during auto-stop 340 (e.g.,between time 6 and time 7), sharply drops as the lead-acid battery 30warm cranks 342 the internal combustion engine 18 (e.g., at time 7), andmicro-cycles after the electrical power stored in the LTO/NMC battery 32is depleted or nearly depleted (e.g., during acceleration 344).

More specifically, in the depicted embodiment, the first switch 286 isclosed and the second switch 288 is open between time 0 and time 3(e.g., key-off 326, cold crank 328, acceleration 330, and cruising 332)and after the LTO/NMC battery 32 discharges to the threshold voltage(e.g., micro-cycling 346 or discharging 348) to enable the lead-acidbattery 30 to supply power to the electrical system 66 by itself.Accordingly, as depicted, the battery system voltage 320 is thelead-acid battery voltage 322 and the second battery voltage 324 remainsrelatively constant during these periods.

On the other hand, the first switch 286 is open and the second switch288 is closed when the LTO/NMC battery 32 captures regenerative power(e.g., regenerative braking 334 and 338) and when the second battery 32provides electrical power by itself. Illustratively, in the depictedembodiment, the first switch 286 is open and the second switch 288 isclosed as the LTO/NMC battery 32 begins supplying power during cruising336 (e.g., before micro-cycling 346) and auto-stop 340 (e.g., beforedischarging 348). Accordingly, as depicted, the battery system voltage320 is the second battery voltage 324 and the lead-acid battery voltage322 remains relatively constants (e.g., 12.9 volts). Additionally, asdescribed above, the first switch 286 may be open to enable thealternator 64 to output the up to maximum charging voltage of theLTO/NMC battery 32 (e.g., 16.8 volts) while protecting the lead-acidbattery 30 from overvoltage.

Once the LTO/NMC battery 32 has discharged to the threshold voltage(e.g., 13.3 volts), as described above, the first switch 286 may closeand the second switch 288 may open (e.g., micro-cycling 346 ordischarging 348). Furthermore, in the depicted embodiment, since thefirst switch 286 is closed and the second switch 288 is open, thelead-acid battery 30 supplies power to warm crank 342 and accelerate344.

Switch Passive—Third Embodiment Partial Voltage Matched

Based on the above description of the first partial voltage matchembodiment, less than the full storage capacity of the second battery 32is utilized to capture regenerative power because the second battery 32discharges until it reaches the threshold voltage. However, in theswitch passive embodiment, because the operation (e.g.,charging/discharging) of the batteries 30 and 32 may be relativelyindependent, the second battery 32 may be enabled to discharge below thethreshold voltage (e.g., lead-acid battery voltage). In other words, thestorage capacity of the second battery 32 may be more fully utilized.Illustratively, FIG. 14C depicts a battery system voltage curve 350(represented by dotted line), a lead-acid battery voltage curve 350, anda second battery voltage curve 352, in accordance with a thirdembodiment. Accordingly, as used herein, the “third embodiment” isintended to describe maintaining the lead-acid battery 30 at a generallyfull charge (e.g., 95-100% state of charge) while maintain the secondbattery 32 generally empty (e.g., 0% state of charge).

Similar to the first partial voltage match battery system voltagedescribed in FIG. 14B, the battery system voltage 350 decreases as thelead-acid battery 30 supplies electrical power to the electrical system66 during key-off 356 (e.g., between time 0 and time 1), sharply dropsas the lead-acid battery cold cranks 358 the internal combustion engine(e.g., at time 1), micro-cycles (e.g., to maintain the lead-acid batterybetween 95-100% state of charge) while the vehicle accelerates 360 andcruises 362 (e.g., between time 1 and time 3), increases as electricalpower is stored in the LTO/NMC battery 32 during regenerative braking364 (e.g., between time 3 and time 4), decreases as the LTO/NMC battery32 supplies electrical power to the electrical system 66 during cruising366 (e.g., between time 4 and time 5), increases as electrical power isagain stored in the LTO/NMC battery 32 during regenerative braking 368(e.g., between time 5 and time 6), decreases as the LTO/NMC battery 32supplies electrical power to the electrical system 66 during auto-stop370 (e.g., between time 6 and time 7), sharply drops to warm crank 372the internal combustion engine 18 (e.g., at time 7), and micro-cyclesafter the electrical power stored in the LTO/NMC battery 32 is depletedor nearly depleted (e.g., during acceleration 374).

More specifically, in the depicted embodiment, the first switch 286 isclosed and the second switch 288 is open between time 0 and time 3(e.g., key-off 356, cold crank 358, acceleration 360, and cruising 362).However, instead of maintain the LTO/NMC battery 32 at approximately 25%state of charge, the LTO/NMC battery 32 is maintained at approximately0% state of charge to utilize the full storage capacity of the secondbattery 32. Accordingly, as depicted, the battery system voltage 352 isthe lead-acid battery voltage 352. As regenerative power is generated(e.g., during regenerative braking 364 and 368), the first switch 286 isopen and the second switch 288 is closed to steer the regenerative powerto the LTO/NMC battery 32. Additionally, the first switch 286 may remainopen and the second switch 288 may remain closed as the LTO/NMC battery32 provides power to the electrical system 66 by itself (e.g., duringcruising 366 and auto-stop 370). Accordingly, as depicted, during theseperiods, the battery system voltage 350 is the second battery voltage354 and the lead-acid battery voltage 352 remains constant (e.g., at12.9 volts). Additionally, as described above, the first switch 286 maybe open to enable the alternator 64 to output up to the maximum chargingvoltage of the LTO/NMC battery 32 (e.g., 16.8 volts) while protectingthe lead-acid battery 30 from overvoltage.

Moreover, as depicted, the LTO/NMC battery 32 may continue to supplypower even after it has discharged to the threshold voltage (e.g.,discharge 376 and 378). For example, at discharge 378, the LTO/NMCbattery 32 discharges until it is depleted (e.g., to 11.8 volts).Comparatively, when lead-acid battery 30 is directly coupled to the bus68, such as in the passive architecture 52 or the semi-passivearchitecture 54B, the lead-acid battery 30 may begin to discharge oncethe battery system voltage nears the lead-acid battery voltage.Accordingly, the switch passive architecture 56 enables the utilizationof the full storage capacity of the second battery 32 by disconnectingthe lead-acid battery 30 when the second battery 32 is discharging. Oncethe LTO/NMC battery 32 is depleted or nearly depleted, the second switch288 may be open and the first switch 286 may be closed to enable thelead-acid battery 30 to supply power by itself (e.g., duringacceleration 374 after discharge 378). Accordingly, as depicted, thebattery system voltage 350 again is the lead-acid battery voltage 352.

Additionally, in the depicted embodiment, both the first switch 286 andthe second switch 288 may be closed to enable both the lead-acid battery30 and the LTO/NMC battery 32 to supply power to the starter 62 to warmcrank the internal combustion engine. More specifically, similar to thenon-voltage match embodiment described in FIG. 14C, the LTO/NMC battery32 still contains stored power. However, because cranking the internalcombustion engine may require a large amount of power (e.g., 5 kW) bothbatteries 30 and 32 may be utilized. In other words, whether to use thelead-acid battery 30, the second battery 32, or both to crank theinternal combustion engine may be determined based on the second batterystate of charge when the engine is to be cranked. More specifically,when the second battery state of charge is greater than a minimum stateof charge, the second battery 32 may crank the internal combustionengine 18 by itself, when the second battery 32 is depleted thelead-acid battery 30 may crank the internal combustion engine 18 byitself, and when the second battery is not depleted but less than theminimum state of charge both the lead-acid battery 30 and the secondbattery 32 may crank the internal combustion engine together.Additionally, in other embodiments, both the first switch 286 and thesecond switch 288 may both be closed to supply power for otheroperations besides cranking.

Switch Passive—Voltage Matched

Utilizing the techniques discussed in relation to the third partialvoltage match embodiment described in FIG. 14C, the voltage matchembodiment may also increase the utilization of the second batterystorage capacity. Illustratively, FIG. 14D depicts a battery systemvoltage curve 380 (represented by dotted line), a lead-acid batteryvoltage curve 382, and a second battery voltage curve 384, which arebased on the voltage characteristics described in FIG. 7. In otherwords, a lead-acid battery 30 and a LTO/LMO battery 32. Thus, thelead-acid battery 30 is generally maintained between 95-100% state ofcharge and the LTO/LMO battery 32 is generally empty (e.g., 0% state ofcharge).

In the depicted embodiment, the first switch 286 is open and the secondswitch 288 is closed between time 0 and time 3 (e.g., key-off 386, coldcrank 388, acceleration 390, and cruising 392) to enable the lead-acidbattery 30 to supply power to the electrical system 66 by itself.Accordingly, as depicted, the battery system voltage 380 is thelead-acid battery voltage 382. During regenerative braking (e.g., 394and 398), the first switch 286 is open and the second switch 288 isclosed to enable the LTO/LMO battery 32 to capture the regenerativepower. Accordingly, as depicted, the battery system voltage 380 is thesecond battery voltage 384 and the lead-acid battery voltage 382 remainsconstant (e.g., 12.9 volts).

Additionally, when the LTO/LMO battery 32 supplies power to theelectrical system 66 (e.g., during cruising 396 or auto-stop 400), thefirst switch 286 may be open and the second switch 288 may be closed.Accordingly, as depicted, the battery system voltage 380 is the secondbattery voltage 384 when the LTO/LMO battery 32 supplies power byitself. Moreover, as depicted, the LTO/LMO battery 32 may continue tosupply power even after it has discharged to the threshold voltage(e.g., 12.9 volts) because the lead-acid battery 30 is disconnected viathe first switch 286 (e.g., discharge 402 and 404). Accordingly, switchpassive embodiment enables the storage capacity of the second battery 32to be more fully be utilized than in the semi-passive and passiveembodiments.

Furthermore, as in the depicted embodiment, the first switch 286 mayclose and the second switch 288 may open once the LTO/LMO battery 32 isdepleted or reaches a minimum state of charge to enable the lead-acidbattery 30 to supply power. Accordingly, because the LTO/LMO battery 32is depleted, the lead-acid battery 30 may warm crank 406 and supplypower during acceleration 408 by itself and the battery system voltage380 is the lead-acid battery voltage 382.

As discussed above with regard to the switch passive embodimentsdescribed in FIGS. 14A-14D, the first switch 286 may be open todisconnect the lead-acid battery 30 when the second battery 32 ischarging (e.g., during regenerative braking) and discharging (e.g.,during cruising or auto-stop). Accordingly, as in the depictedembodiments, the lead-acid battery 30 may be maintained at a relativelyconstant voltage (e.g., 12.9 volts). Comparatively, with regard to thepassive embodiments and semi-passive embodiments, the lead-acid battery30 may be put at a higher voltage when the second battery 32 ischarging/discharging because it is directly connected to the bus 68. Inother words, the lifespan of the lead-acid battery 30 may be bettercontrolled by limiting its exposure to high charging voltages (e.g.,overvoltage), for example during regenerative braking. Accordingly, theoverall cost of a switch passive battery system 56 may be reduced.

Based on the various embodiments of switch passive battery systems 56described above, the control algorithm utilized by the battery controlunit 34 may be more complex than the algorithm utilized for semi-passivebattery systems 54. More specifically, in addition to controlling thealternator 64, the battery control unit 34 may close and open both thefirst switch 286 and the second switch 288 to control the operation ofthe switch passive battery system 56. As described above, the firstswitch may be closed when the lead-acid battery 30 supplies power andopen otherwise, for example to enable the second battery 32 to be moreefficiently charged while protecting the lead-acid battery 30 fromovervoltage. Additionally, the second switch 288 may be closed when thesecond battery 32 is charging or discharging and may be open otherwise.Accordingly, the battery control unit 34 may turn on/off the alternator64 as well as open/close the first switch 286 and the second switch 288to maintain each of the batteries 30 and 32 at their respective targetstates of charge. Furthermore, in some situations, both the first switch286 and the second switch 288 may both be closed, for example to warmcrank, based on the power requirements of the particular vehicleoperation and the state of charge of the batteries 30 and 32. Moreover,although not described in the embodiments described above, in otherembodiments, both the first switch 286 and the second switch 288 may beopen to enable the alternator 64 to supply power to the electricalsystem 66 by itself.

Semi-Active and Active Architectures for Dual Chemistry Batteries

As can be appreciated in the passive 52, semi-passive 54, and switchpassive 54 embodiments described above, a variable voltage alternatormay be used to charge the batteries 30 and 32. For example, when thelead acid battery 30 and the second battery 32 exhibit non-voltagematched characteristics as described in FIG. 5, the alternator 64 mayincrease its voltage output to 16.6 volts or more to charge the NMCbattery 32. In other words, the alternator may be a variable voltagealternator that outputs a higher voltage during regenerative braking anda lower voltage otherwise. However, alternators are often constantvoltage alternators, such as an alternator that outputs a constant 13.3,14.4, or 14.8 volts. Accordingly, to minimize the modifications toexisting vehicle platforms, the present techniques may be adapted toutilize a constant voltage variable power alternator. More specifically,a semi-active 58 or active architecture 60 may be utilized. In otherembodiments, a variable alternator may be used, which may reduce thevoltage boosting (e.g., by a DC/DC converter) to charge/discharge thebatteries. In such embodiments, the semi-active 58 and activearchitectures 60 may function similar to the semi-passive 54 and switchpassive architectures 56, respectively.

Generally, replacing the switches (e.g., 188, 286, and 288) in thesemi-passive 54 and switch-passive 56 architectures with DC/DCconverters results in the semi-active 58 and active 60 architecturesrespectively. Illustratively, FIG. 15A depicts an embodiment of asemi-active architecture 58A with a DC/DC converter 410A includedbetween the lead-acid battery 30 and the bus 68, and FIG. 15B depicts anembodiment of a semi-active architecture 58B with a DC/DC converter 410Bincluded between the second battery 32 and the bus 68. Additionally,FIG. 19 depicts an embodiment of an active architecture 60 with a firstDC/DC converter 412 included between the lead-acid battery 30 and thebus 68, and a second DC/DC converter 414 included between the secondbattery 32 and the bus 68. For the following illustrative embodiments,the alternator 64 will be described as a 13.3 volt constant voltagealternator. However, it should be appreciated that in other embodimentsthe alternator 64 may output a constant voltage between 7-18 volts.

The DC/DC converters (e.g., 410, 412, and 414) may function similar tothe switches to selectively connect/disconnect the batteries 30 or 32from the bus 68. In some embodiments, a DC/DC converter may disconnect abattery by outputting zero current, for example by closing the internalswitch in a boost converter or opening the internal switch in a buckconverter. Additionally, the DC/DC converters may step up or step downthe voltage input to the battery or the voltage output by the battery.Illustratively, a first example will be described in regards tobatteries 30 and 32 that exhibit the non-voltage match characteristicsdescribed in FIG. 5. As described in FIG. 5, the voltage of the NMCbattery 32 ranges between 13.3 to 16.6 volts. Accordingly, to charge theNMC battery 32 with the 13.3 bus voltage, the DC/DC converter (e.g., 410or 414) may step up the 13.3 volts input from the bus 68 to the NMCbattery voltage (e.g., between 13.3 and 16.6 volts). A second examplewill be described in regards to batteries 30 and 32 that exhibit thevoltage match characteristics described in FIG. 7. As described in FIG.7, the voltage of the LTO/LMO battery 32 ranges between 11.7 and 13.2volts. Accordingly, to discharge the LTO/LMO battery 32, the DC/DCconverter (e.g., 410 or 414) may step up the voltage output by theLTO/LMO battery 32 to the bus voltage (e.g., 13.3 volts). In otherwords, the battery control unit 34 may selectively connect anddisconnect each battery 30 or 32 to bus 68 by controlling the operationof the DC/DC converters (e.g., 410, 412, and 414).

In both of the examples described above, the DC/DC converter may be aboost converter. More specifically, in the first example, a boostconverter may step up the bus voltage to charge the NMC battery 32. Inthe second example, a boost converter may step up the voltage output bythe LTO/LMO battery 32 to supply power to the electrical system 66. Inother embodiments, depending on the battery chemistries selected (e.g.,non-voltage matched, partial voltage matched, or voltage matched), theDC/DC converter (e.g., 410, 412, and 414) may be a boost converter, abuck converter, or a bi-directional converter (e.g., boost-buckconverter). For example, to further conform with existing vehicledesigns, a buck converter may be utilized in the first example to stepdown the voltage output by the NMC battery 32 when discharging toapproximately the bus voltage (e.g., 13.3 volts). Accordingly, to stepup the voltage input to the NMC battery 32 when charging and to stepdown the voltage output by the NMC battery 32 when discharging, abi-directional converter, such as a boost-buck converter, may be used.

In addition to enabling a battery 30 or 32 to be selectively connectedand disconnected from the bus 68, the DC/DC converters (e.g., 410, 412,and 414) may provide additional control over the operation of thebatteries. More specifically, a DC/DC converter may set the voltageoutput by the DC/DC converter. For example, in the first exampledescribed above, the DC/DC converter (e.g., 410, 412, and 414) mayselectively step up the bus voltage to more optimally charge the NMCbattery 32. Similarly, in the second example described above, the DC/DCconverter may selectively output a voltage to the bus 68 to match thebus voltage and/or the voltage components in the electrical system 66are designed to optimally function with. Additionally, the DC/DCconverters (e.g., 410, 412, and 414) may limit the current that flowsthrough the DC/DC converter. In some embodiments, this may enablecontrol of the electrical power output to the vehicle.

It should be noted that with the increased functionality provided by theuse of a DC/DC converter (e.g., 410, 412, and 414), DC/DC converters aregenerally not 100% efficient. In other words, some losses may beexperience as each DC/DC converter adjusts (i.e., steps up or stepsdown) voltage. Generally, the efficiency of a DC/DC converter may bebetween 75-98% efficient. Accordingly, to reduce the losses that mayresult from use of a DC/DC converter, it may be beneficial to bypass theDC/DC converter. Illustratively, a block of a DC/DC converter (e.g.,410, 412, and 414) with an output bypass is described in FIG. 16 and ablock diagram of a DC/DC converter (e.g., 410, 412, and 414) with aninput bypass is depicted in FIG. 17.

As depicted in both FIGS. 16 and 17, a converter switch 416 may selectbetween a bypass path 418 and a converter path 420. More specifically,as described in FIG. 16, the converter switch 416 may select theconverter path 420 when a battery 30 or 32 is charging. For example, asdiscussed above in the first example, the bus voltage may be stepped upto charge a NMC battery 32. Additionally, the switch 416 may select thebypass path 418 when a battery 30 or 32 is discharging. For example,because the voltage of a NMC battery 32 (e.g., between 13.3 and 16.6volts) may be greater than the bus voltage (e.g., 13.3 volts), the NMCbattery 32 will discharge due to its higher voltage. In other words, thebypass path 418 enables current to flow from the higher battery voltageto the lower bus voltage.

Conversely, as depicted in FIG. 17, the converter switch 416 may selectconverter path 420 when a battery 30 or 32 is discharging. For example,as discussed above in the second example, the voltage output by aLTO/LMO battery 32 may be stepped up to the bus voltage. Additionally,the converter switch 416 may select the bypass path 418 when a battery30 or 32 is charging. For example, because the bus voltage (e.g., 13.3volts) may be greater than the voltage of a LTO/LMO battery 32 (e.g.,between 11.7 and 13.2 volts), the bus voltage will charge the LTO/LMObattery 32 due to its higher voltage. In other words, the bypass path418 enables current to flow from the higher bus voltage to the lowersecond battery voltage. As can be appreciated, the control algorithmutilized by the battery control unit 34 may control the operation of theconverter switch 416.

With the proceeding in mind, FIGS. 18A-18D describe the illustrativevoltage of the semi-active battery system 58B, depicted in FIG. 15B, inrelation to the hypothetical vehicle operation described above. FIGS.18A-18D are XY plots that each includes a battery system voltage curvethat describes the dynamic voltage of the semi-active battery system 58Band a second battery voltage curve that describes the dynamic voltage ofthe second battery 32 between time 0 and time 8, in which voltage is onthe Y-axis and time is on the X-axis. More specifically, FIG. 18Adescribes a semi-active battery system 58B with a non-voltage matchedbattery pairing, FIG. 18B describes a semi-active battery system 58Bwith the first embodiment of a partial voltage matched battery pairing,FIG. 18C describes a semi-active battery system 58B with the secondembodiment of a partial voltage matched battery pairing, and FIG. 18Ddescribes a semi-active battery system 58B with a voltage matchedbattery pairing. As should be appreciated, since the lead-acid battery30 is directly connected to the bus 68, the battery system voltage willbe the same as the lead-acid battery voltage.

Semi-Active Architecture—Non-Voltage Matched

As described above, FIG. 18A describes a semi-active battery system 58Bwhen the batteries 30 and 32 are non-voltage matched. FIG. 18A depicts abattery system voltage curve 422 and a second battery voltage curve 424.More specifically, the voltage curves 422 and 424 are based on thevoltage characteristics described in FIG. 5. In other words, a lead-acidbattery 30 and a NMC battery 32.

In the depicted embodiment, the lead-acid battery 30 supplies power tothe electrical system 66 by itself during key-off 426 and to cold crank428 the internal combustion engine. Accordingly, as depicted, thebattery system voltage 422 decreases as the lead-acid battery state ofcharge decreases and sharply drops as the lead-acid battery 30 coldcranks 428. As the vehicle accelerates 430 and cruises 432, thealternator 64 periodically outputs 13.3 volts to micro-cycle thelead-acid battery 30 (e.g., to maintain between 95-100% state ofcharge). More specifically, the lead-acid battery 30 voltage is raisedto the voltage output by the alternator 64 when the alternator 64charges the lead-acid battery 30. For example, when the lead-acidbattery 30 reaches a minimum target state of charge (e.g., 95% state ofcharge), the alternator 64 outputs 13.3 volts to charge the lead-acidbattery 30 to a maximum target state of charge (e.g., 100% state ofcharge). Once the maximum target state of charge is reached, thealternator 64 turns off and the lead-acid battery 30 supplies power.Accordingly, as depicted, the battery system voltage 422 cycles betweenapproximately 13.3 volts and 12.8 volts as the lead-acid battery 30 ismicro-cycled. Comparatively, in the embodiments described above (e.g.,passive, semi-passive, and switch passive), the variable voltagealternator may output approximately 12.9 volts to micro-cycle thelead-acid battery 30 between 12.9 volts (e.g., 100% state of charge) and12.8 volts (e.g., 95% state of charge). Additionally, the NMC battery 32may be disconnected via the DC/DC converter 410B during this period(e.g., between time 0 to time 3). Accordingly, as depicted, the secondbattery voltage 424 remains relatively constant (e.g., 13.3 volts).

In the depicted embodiment, to reduce the electrical power cost of thesemi-active battery system 58, the DC/DC converter 410B may include abypass path 418 as described in FIG. 16 (e.g., output bypass). Morespecifically, utilizing a bypass path 418 may reduce the cost of theDC/DC converter 410B because such a DC/DC converter may cost less than asimilar bi-directional DC/DC converter (e.g., a boost-buck converter)and may reduce the losses associated with adjusting (e.g., stepping upor stepping down) voltage in the DC/DC converter. Accordingly, in thedepicted embodiment, when the NMC battery 32 is charging, for exampleduring regenerative braking 434 or 436, the converter path 420 may beselected. More specifically, as regenerative power is generated, thealternator 64 outputs a constant 13.3 volts. To charge the NMC battery32 with the constant 13.3 volts, the battery control unit 34 may controlthe DC/DC converter 410B to step up the voltage to the second batteryvoltage 424 (e.g., between 13.3-16.6 volts). In other words, the DC/DCconverter 410B may be a boost converter. Accordingly, as depicted, thesecond battery voltage 424 increases as the NMC battery 32 capturesregenerative power while the battery system voltage 422 is maintained ata relatively constant the 13.3 volts output by the alternator 64.

Moreover, in some embodiments, the DC/DC converter 410B may enable thesecond battery 32 to be more efficiently charged while protecting thelead-acid battery 30 from overvoltage. For example, in the depictedembodiment to increase the charge power acceptance rate of the NMCbattery 32, DC/DC converter 410B may boost the bus voltage up to themaximum charging voltage of the NMC battery 32 (e.g., 16.8 volts), whichmay be above the maximum charging voltage of the lead-acid battery 30(e.g., overvoltage). However, since the bus voltage is unchanged, thelead-acid battery 30 may be protected from overvoltage.

On the other hand, when the NMC battery 32 supplies power, for exampleduring cruising 438 or auto-stop 440, the battery control unit 34 mayselect the bypass path 418 via the converter switch 416 to enable theNMC battery 32 to discharge based on its higher voltage. Accordingly, asdepicted, the battery system voltage 422 is the second battery voltage424 during these periods.

As should be appreciated, when the bypass path 418 is selected, thebattery system functions similarly to the passive battery systemembodiments described above. In other words, the NMC battery 32 maysupply power to the electrical system 66 until depleted or nearlydepleted. Accordingly, as depicted, the lead-acid battery 30 along withthe NMC battery 32 may supply power to cold crank 442 the internalcombustion engine 18. Once depleted, the NMC battery 32 may bedisconnected via the DC/DC converter 410B and the lead-acid battery 30may supply electrical power to the electrical system 66 by itself.Accordingly, as depicted, the battery system voltage 422 decreases asthe NMC battery 32 continues to supply power to the electrical system 66and micro-cycles with the lead-acid battery 30 after the NMC battery 32is depleted 444 (e.g., during acceleration 446),

Semi-Active Architecture—First Embodiment Partial Voltage Matched

As described above, FIG. 18B describes a semi-active battery system 58Bwhen the batteries 30 and 32 are partial voltage matched, in accordancewith the first embodiment. FIG. 18B depicts a battery system voltagecurve 448 and a second battery voltage curve 450. More specifically, thevoltage curves 448 and 450 are based on the voltage characteristicsdescribed in FIG. 6. In other words, a lead-acid battery 30 and aLTO/NMC battery 32.

In the present embodiment, similar to the first partial voltage matchpassive, semi-passive, and switch passive embodiments described above,the lead-acid battery 30 may be maintained at approximately 95-100%state of charge. However, because the alternator 64 to micro-cycle thelead-acid battery 30 up to 13.3 volts, the threshold voltage may be 13.3volts. Accordingly, in the present embodiment, the LTO/NMC battery 32may be maintained at approximately 50% state of charge (e.g., 13.3volts).

Similar to the non-voltage match embodiment described in FIG. 18A, thebattery system voltage 448 decreases as the lead-acid battery 30supplies power to the electrical system 66 during key-off 452, sharplydrop as the lead-acid battery 30 cold cranks 454 the internal combustionengine, and micro-cycles as the lead-acid battery is micro-cycled (e.g.,to maintain between 95-100% state of charge).

The depicted embodiment also utilizes the DC/DC converter 410B similarto the one described in FIG. 16 (e.g., output bypass) with a bypass path418 to reduce the cost of the semi-active battery system 58. Thus, whenregenerative power is generated, the converter path 420 is selected tostep up the voltage output by the alternator 64 and charge the LTO/NMCbattery 32. Accordingly, as depicted, the battery system voltage remainsconstant (e.g., 13.3 volts) as the alternator 64 generates regenerativepower during regenerative braking 460 and 464. More specifically, asdiscussed above, the DC/DC converter 410B steps up the voltage output bythe alternator (e.g., 13.3 volts) to the second battery voltage 450(e.g., between 13.3-16 volts). Additionally, as described above, theDC/DC converter 410B may enable the second battery 32 to be charge at avoltage up to the maximum charging voltage of the LTO/NMC battery 32(e.g., 16.8 volts) while protecting the lead-acid battery 30 fromovervoltage.

On the other hand, when the LTO/NMC battery 32 is supplying power to theelectrical system 66, the bypass path 418 is selected to enable theLTO/NMC battery 32 to discharge based on its higher voltage (e.g.,13.3-16 volts). Accordingly, as depicted, the battery system voltage 448is the second battery voltage 450.

The LTO/NMC battery 32 may continue supplying power until it reaches thethreshold voltage (e.g., 13.3 volts). Once the threshold voltage isreached, the LTO/NMC battery 32 may be disconnected to enable thelead-acid battery 30 to supply power. Accordingly, as depicted, when theLTO/NMC battery 32 reaches the threshold voltage during cruising 462,the battery system voltage 448 micro-cycles 466 as the lead-acid battery30 is micro-cycled by the alternator 64 (e.g., between 95-100% state ofcharge). Additionally, when the LTO/NMC battery 32 reaches the thresholdvoltage during auto-stop 468, the battery system voltage 448 decreasesas the lead-acid battery 30 supplies power. Furthermore, after theLTO/NMC battery 32 reaches the threshold voltage, the lead-acid battery30 may cold crank 470 and supply power during acceleration 472.

Semi-Active Architecture—Third Embodiment Partial Voltage Matched

Based on the above description of the first embodiment of thesemi-active battery system 58B with partial voltage matched batteries,the storage capacity of the LTO/NMC battery 32 may be further limitedbecause the threshold voltage is set to 13.3 volts. Accordingly, similarto the passive and semi-passive embodiments described above, thethreshold voltage may be lowered by lowering the voltage output by thealternator 64. Additionally or alternatively, a bi-direction converter(e.g., boost-buck converter) may be used. More specifically, aboost-buck converter may operate bi-directionally and both step up orstep down the input voltage. Illustratively, FIG. 18C depicts a batterysystem voltage curve 474 and a second battery voltage curve 476 when thebatteries 30 and 32 are partial voltage matched, in accordance with thethird embodiment.

Similar to the first partial voltage match battery system described inFIG. 18B, the battery system voltage 474 decreases as the lead-acidbattery 30 supplies electrical power to the electrical system 66 duringkey-off 478 (e.g., between time 0 and time 1), sharply drops as thelead-acid battery 30 cold cranks 480 the internal combustion engine(e.g., at time 1), and micro-cycles (e.g., to maintain the lead-acidbattery between 95-100% state of charge) while the vehicle accelerates482 and cruises 484 (e.g., between time 1 and time 3). Additionally,instead of maintaining the LTO/NMC battery 32 at approximately 50% stateof charge as in FIG. 18B, the LTO/NMC battery 32 is maintained atapproximately 0% state of charge by disconnecting the second battery viathe DC/DC converter 410B.

When regenerative power is generated, for example during regenerativebraking 486 or 488, the alternator 64 outputs a constant voltage (e.g.,13.3 volts). Accordingly, as depicted, the battery system voltage 474 ismaintained at a relatively constant 13.3 volts. Additionally, theregenerative power generated by the alternator 64 charges the LTO/NMCbattery 32. More specifically, when the second battery voltage 476 isless than the bus voltage (e.g., voltage output by the alternator), forexample during charging 490 or 492, the DC/DC converter 410B may set thevoltage (e.g., step down the bus voltage (e.g., 13.3 volts) to thesecond battery voltage (e.g., between 11.7-13.2 volts)) to charge theLTO/NMC battery 32. Once the second battery voltage 476 reaches thevoltage output by the alternator 64, the DC/DC converter may step up thebus voltage (e.g., 13.3) to the second battery voltage (e.g., 13.3-16volts) and charge the LTO/NMC battery 32. Additionally, as describedabove, the DC/DC converter 410B may enable the second battery 32 to becharge at a voltage up to the maximum charging voltage of the LTO/NMCbattery 32 (e.g., 16.8 volts) while protecting the lead-acid battery 30from overvoltage.

When the LTO/NMC battery 32 supplies power to the electrical system 66,for example during cruising 494 or auto-stop 496, the DC/DC converter410B may maintain the bus voltage at approximately the same voltageoutput by the alternator 64 (e.g., 13.3 volts). For example, when thesecond battery voltage 476 is greater than 13.3 volts (e.g., discharging498 and auto-stop 500), the DC/DC converter 410B may step down thevoltage. On the other hand, when the second battery voltage is less than13.3 volts (e.g., discharging 502 and 503), the DC/DC converter 410B maystep up the voltage. Accordingly, as depicted, the battery systemvoltage 474 is maintained at 13.3 volts during this period. Furthermore,the LTO/NMC battery 32 may continue to supply power until depleted. Forexample, as depicted, the LTO/NMC battery 32 may supply power duringacceleration 504 until depleted and may supplement the lead-acid battery30 to warm crank 506 the internal combustion engine 18.

Semi-Active Architecture—Voltage Matched

As described above, FIG. 18D depicts a battery system voltage curve 508that describes the semi-active battery system voltage and a secondbattery voltage curve 510 when the batteries 30 and 32 are voltagematched. More specifically, the voltage curves 508 and 510 are based onthe voltage characteristics described in FIG. 7, In other words, alead-acid battery 30 and a LTO/LMO battery 32. Additionally, similar tothe third partial voltage match embodiment described in FIG. 18C, in thepresent embodiment, the lead-acid battery 30 may generally be maintainedbetween 95-100% state of charge and the LTO/LMO battery 32 may bemaintained generally at 0% state of charge even though the voltage(e.g., 11.7 volts) is less than the threshold voltage (e.g., 13.3 volts)to enable the second battery to utilize its full storage capacity tocapture regenerative power.

Similar to the partial voltage match embodiment described in FIG. 18C,the battery system voltage 508 decreases as the lead-acid battery 30supplies electrical power to the electrical system 66 during key-off 512(e.g., between time 0 and time 1), sharply drops as the lead-acidbattery 30 cold cranks 514 the internal combustion engine (e.g., at time1), and micro-cycles (e.g., to maintain the lead-acid battery between95-100% state of charge) while the vehicle accelerates 516 and cruises518 (e.g., between time 1 and time 3). Additionally, the LTO/LMO battery32 is maintained at approximately 0% state of charge (e.g., 11.7 volts)by disconnecting the second battery via the DC/DC converter 410B.

When regenerative power is generated, for example during regenerativebraking 520 or 522, the alternator 64 outputs a constant voltage (e.g.,13.3 volts). Accordingly as depicted, the battery system voltage 508 ismaintained at a constant 13.3 volts. Additionally, the regenerativepower generated by the alternator 64 charges the LTO/LMO battery 32. Inthe depicted embodiment, the second battery voltage 510 ranges between11.7 volts (e.g., at 0% state of charge) and 13.2 volts (e.g., at 100%state of charge). In other words, the second battery voltage 510 is lessthan the 13.3 volts output by the alternator 64. Accordingly, in someembodiments, the DC/DC converter 410B may set the voltage (e.g., stepdown the bus voltage (e.g., 13.3 volts) to the second battery voltage(e.g., between 11.7-13.2 volts)) to charge the LTO/LMO battery 32.

When the LTO/LMO battery 32 supplies power to the electrical system, forexample during cruising 524 or auto-stop 526, the DC/DC converter 410Bmay maintain the bus voltage at approximately the same voltage as outputby the alternator 64. More specifically, since the second batteryvoltage 510 (e.g., between 11.8-13.2 volts) is less than the voltageoutput by the alternator 64 (e.g., 13.3 volts), the DC/DC converter 410Bmay step up the voltage output by the LTO/LMO battery 32. Accordingly,as depicted, the battery system voltage 508 is maintained generally at13.3 volts. Furthermore, the LTO/LMO battery 32 may supply power untildepleted. For example, as depicted, when the LTO/LMO battery 32 isdepleted during auto-stop 526, the battery system voltage 508 decreasesas the lead-acid battery 30 supplies power. Furthermore, after theLTO/LMO battery 32 is depleted, the lead-acid battery 30 supplies powerto cold crank 528 and during acceleration 530.

In some embodiments described above, the DC/DC converter 410B isdescribed as a bi-directional converter (e.g., boost-buck) that stepsdown the bus voltage to charge the second battery 32 and steps up thesecond battery voltage 510 to supply power to the electrical system 66.Additionally or alternatively, the DC/DC converter 410B may be aconverter with a bypass path similar to the DC/DC converter described inFIG. 17 (e.g., input bypass). More specifically, the bypass path 418 maybe selected when the LTO/LMO battery 32 is being charged to enablecurrent to flow from the higher bus voltage (e.g., 13.3 volts) to thelower second battery voltage (e.g., between 11.8-112 volts). On theother hand, the converter path 420 may be selected when the LTO/LMObattery 32 is supplying power to step up the voltage output by thesecond battery.

Based on the various embodiments of the semi-active battery systems 58described above, the control algorithm utilized by the battery controlunit 34 may be more complex than the algorithm utilized for semi-passivebattery systems 54. More specifically, in addition to controlling thealternator 64, the battery control unit 34 may control the operation ofthe DC/DC converter 410, which may include opening/closing internalswitches in the DC/DC converter 410. For example, in some embodiments,the battery control unit 34 may utilize the DC/DC converter 410B toenable the second battery 32 to be more optimally charged (e.g., with ahigher charging voltage) while protecting the lead-acid battery 30 fromovervoltage. Accordingly, the battery control unit 34 may turn on/offthe alternator 64 as well as open/close the internal switches in theDC/DC converter 410 to maintain each of the batteries 30 and 32 at theirrespective target states of charge. Additionally, the battery controlunit 34 may control other operational parameter with the DC/DC converter410, such as limiting current or voltage. Furthermore, when a converterwith a bypass path (e.g., as described in FIGS. 16 and 17) is utilized,the battery control unit 34 may also control the operation of theconverter switch 416 that selectively switches between the bypass path418 and the converter path 420.

As described above, replacing the switches 286 and 288 in a switchbattery system 56 with the first DC/DC converter 412 and the secondDC/DC converter 414 results in an active battery system 60. As will bedescribed in more detail below, including the first DC/DC converter 412to selectively connect/disconnect the lead-acid battery 30 from the bus68 may enable the battery system voltage to be generally maintained at aconstant voltage (e.g., 13.3 volts) for the duration of the operation ofthe vehicle (e.g., between time 0 and time 8).

With the proceeding in mind, FIGS. 20A-20D describe the illustrativevoltage of the active battery system 60 in relation to the hypotheticalvehicle operation described above. FIGS. 20A-20D are XY plots that eachincludes a voltage curve that describes the dynamic voltage of theactive battery system 60, a lead-acid battery voltage curve thatdescribes the dynamic voltage of the lead-acid battery 30, and a secondbattery voltage curve that describes the dynamic voltage of the secondbattery 32 between time 0 and time 8, in which voltage is on the Y-axisand time is on the X-axis. More specifically, FIG. 20A describes anactive battery system 60 with a non-voltage matched battery pairing,FIG. 20B describes an active battery system 60 with the first embodimentof a partial voltage matched battery pairing, FIG. 20C describes anactive battery system 60 with the third embodiment of a partial voltagematched battery pairing, and FIG. 20D describes an active battery system60 with a voltage matched battery pairing.

Active Architecture—Non-Voltage Matched

As described above, FIG. 20A depicts a battery system voltage curve 532,a lead-acid battery voltage curve 534, and a second battery voltagecurve 424 when the lead-acid battery 30 and the second battery 32 arenon-voltage matched. More specifically, the voltage curves 532, 534, and536 are based on the voltage characteristics described in FIG. 5. Inother words, a lead-acid battery 30 and a NMC battery 32. Similar to thenon-voltage match embodiments described above, the lead-acid battery 30may be maintained generally between 95-100% state of charge and the NMCbattery 32 may be maintained generally at approximately 0% state ofcharge.

In the depicted embodiment, the lead-acid battery 30 supplies power tothe electrical system 66 by itself during key-off 538, cold crank 540,acceleration 542, and cruising 544. More specifically, the lead-acidbattery voltage 534 decreases as the state of charge decreases duringkey-off 538, sharply drops to cold crank 540 the internal combustionengine, and micro-cycles (e.g., between 13.3 volts and 12.8 volts)during acceleration 542 and cruising 544. During this period (e.g.,between time 0 and time 3), the lead-acid battery voltage 534 may bestepped up to a constant voltage (e.g., 13.3 volts) by the first DC/DCconverter 412 (e.g., boost converter). Accordingly, as depicted, thebattery system voltage 532 is generally maintained at a constant 13.3volts. Additionally, the NMC battery 32 may be maintained atapproximately 0% state of charge and disconnected via the second DC/DCconverter 414.

As regenerative power is generated, for example during regenerativebraking 546 or 548, the alternator 64 outputs a constant voltage (e.g.,13.3 volts). Accordingly, as depicted, the battery system voltage 532 ismaintained generally at a constant 13.3 volts. Additionally, to chargethe NMC battery 32 with the constant 13.3 volts, the second DC/DCconverter 414 may step up the voltage to match the second batteryvoltage 536. Furthermore, the lead-acid battery 30 may be disconnectedvia the first DC/DC converter 412. In other embodiments, the first DC/DCconverter 412 may maintain the lead-acid battery 30 at its targetoperating point by controlling the voltage. Accordingly, as depicted,the second battery voltage 536 increases as the NMC battery 32 capturesregenerative power and the lead-acid battery voltage 534 remainsrelatively constant (e.g., 12.9 volts).

Moreover, in some embodiments, the DC/DC converters 412 and 414 mayenable the second battery 32 to be more efficiently charged whileprotecting the lead-acid battery 30 from overvoltage. For example, inthe depicted embodiment to increase the charge power acceptance rate ofthe NMC battery 32, the second DC/DC converter 414 may boost the busvoltage up to the maximum charging voltage of the NMC battery 32 (e.g.,16.8 volts), which may be above the maximum charging voltage of thelead-acid battery 30 (e.g., overvoltage). However, the first DC/DCconverter 412 may control the voltage applied to the lead-acid battery30 to protect the lead-acid battery 30 from overvoltage.

As the NMC battery 32 supplies power to the electrical system 66, forexample during cruising 550 or auto-stop 552, the second DC/DC converter414 may step down the second battery voltage 536 to match the voltageoutput by the alternator 64. Accordingly, as depicted, the secondbattery voltage 536 decreases as the NMC battery 32 supplies power andthe battery system voltage 532 is maintained at 13.3 volts. Furthermore,the NMC battery 32 may continue supplying power until depleted.Accordingly, as depicted, the NMC battery 32 supplies power to warmcrank 554 the internal combustion engine and during acceleration 556.Once depleted, the NMC battery 32 may be disconnected via the secondDC/DC converter 414 and the lead-acid battery may be connected via thefirst DC/DC converter 412 to supply power to the electrical system 66.

Active Architecture—First Embodiment Partial Voltage Matched

As described above, FIG. 20B describes an active battery system when thebatteries 30 and 32 are partial voltage matched, in accordance with thefirst embodiment. FIG. 20B depicts a battery system voltage curve 558, alead-acid battery curve 560, and a second battery voltage curve 562.More specifically, the voltage curves 558, 560, and 562 are based on thevoltage characteristics described in FIG. 6. In other words, a lead-acidbattery 30 and a LTO/NMC battery 32. Similar to the first partialvoltage match embodiments described above, the lead-acid battery 30 maybe maintained generally between 95-100% state of charge and the LTO/NMCbattery 32 may be generally maintained above the threshold voltage(e.g., 50% state of charge).

Operationally, the present embodiment may be similar to the non-voltagematched embodiment described in FIG. 20A. More specifically, thelead-acid battery 30 supplies power to the electrical system 66 byitself during key-off 564, cold crank 566, acceleration 568, andcruising 570. During this period (e.g., between time 0 and time 3), thelead-acid battery voltage 560 may be stepped up to a constant voltage(e.g., 13.3 volts) by the first DC/DC converter 412 (e.g., boostconverter) and the LTO/NMC battery 32 may be maintained at approximately50% state of charge and disconnected via the second DC/DC converter 414.Accordingly, as depicted, the battery system voltage 558 and the secondbattery voltage 562 remain relatively constant at approximately 13.3volts, Additionally, as regenerative power is generated (e.g.,regenerative braking 572 or 574), the alternator 64 outputs a constantvoltage (e.g., 13.3 volts), the second DC/DC converter 414 steps up thevoltage to match the second battery voltage 562, and the lead-acidbattery 30 is disconnected via the first DC/DC converter 412.Accordingly, as depicted, the battery system voltage 558 is maintainedgenerally at a constant 13.3 volts, the second battery voltage 562increases as the LTO/NMC battery 32 captures regenerative power, and thelead-acid battery voltage 534 remains relatively constant (e.g., 12.9volts). Additionally, as described above, the DC/DC converters 412 and414 may enable the second battery 32 to be charge at a voltage up to themaximum charging voltage of the LTO/NMC battery 32 (e.g., 16.8 volts)while protecting the lead-acid battery 30 from overvoltage.

Furthermore, as the LTO/NMC battery 32 supplies power to the electricalsystem 66 (e.g., during cruising 576 or auto-stop 578), the second DC/DCconverter 414 steps down the second battery voltage 562 to match thevoltage output by the alternator 64. Accordingly, as depicted, thesecond battery voltage 562 decreases as the LTO/NMC battery 32 suppliespower and the battery system voltage 532 is maintained at 13.3 volts.

Furthermore, the LTO/NMC battery 32 may continue supplying power untilthe second battery voltage 562 reaches the threshold voltage (e.g., 13.3volts). Once the threshold voltage is reached, the LTO/NMC battery 32may be disconnected via the second DC/DC converter 414 and the lead-acidbattery 30 may be connected via the first DC/DC converter 412 to enablethe lead-acid battery 30 to supply power. For example, as depicted, whenthe threshold voltage is reached during cruising 576, the lead-acidbattery 30 may be micro-cycled 580. Additionally, when the thresholdvoltage is reached during auto-stop 578, the lead-acid battery state ofcharge may decrease as the lead-acid battery 30 discharges 582.Furthermore, since the second battery voltage 562 has reached thethreshold voltage, the lead-acid battery may supply power to theelectrical system 66 during warm crank 584 and acceleration 586. Duringthis period, the first DC/DC converter 412 may step up the voltageoutput by the lead-acid battery 30 to match the voltage output by thealternator 64. Accordingly, as depicted, the battery system voltage 558remains constant at 13.3 volts.

Active Architecture—Third Embodiment Partial Voltage Matched

As with the first embodiment of the semi-active battery system withpartial voltage matched batteries described in FIG. 18B, the storagecapacity of the LTO/NMC battery 32 may be limited because the thresholdvoltage is increased to 13.3 volts. Accordingly, a bi-directionconverter (e.g., boost-buck converter) may similarly be used.Illustratively, FIG. 20C depicts a battery system voltage curve 588, alead-acid battery voltage curve 590, and a second battery voltage curve592 when the batteries 30 and 32 are partial voltage matched, inaccordance with the third embodiment. As in the semi-active embodiment,the lead-acid battery 30 may be generally maintained between 95-100%state of charge and the LTO/NMC battery 32 may generally be maintainedat 0% state of charge.

Similar to the first partial voltage match battery system described inFIG. 20B, the lead-acid battery 30 supplies power to the electricalsystem 66 by itself during key-off 594, cold crank 596, acceleration598, and cruising 600. During this period (e.g., between time 0 and time3), the lead-acid battery voltage 590 may be stepped up to a constantvoltage (e.g., 13.3 volts) by the first DC/DC converter 412 (e.g., boostconverter) and the LTO/NMC battery 32 may be maintained at approximately0% state of charge and disconnected via the second DC/DC converter 414.Accordingly, as depicted, the battery system voltage 588 remainsrelatively constant at 13.3 volts.

When regenerative power is generated, for example during regenerativebraking 602 or 604, the alternator 64 outputs a constant voltage (e.g.,13.3 volts). Accordingly, as depicted, the battery system voltage 588 ismaintained at a relatively constant 113 volts. To charge the LTO/NMCbattery 32, when the second battery voltage 592 is less that the busvoltage (e.g., charging 606 or 608), the second DC/DC converter 414 maystep down the bus voltage (e.g., 13.3 volts) to the second batteryvoltage 592. Additionally, when the second battery voltage 592 isgreater than the bus voltage, the second DC/DC converter 414 may step upthe bus voltage to the second battery voltage 592. Furthermore, asdescribed above, the DC/DC converters 412 and 414 may enable the secondbattery 32 to be charge at a voltage up to the maximum charging voltageof the LTO/NMC battery 32 (e.g., 16.8 volts) while protecting thelead-acid battery 30 from overvoltage.

When the LTO/NMC battery 32 supplies power to the electrical system 66,for example during cruising 610 or auto-stop 612, the second DC/DCconverter 414 may maintain the bus voltage at approximately the voltageoutput by the alternator 64 (e.g., 13.3 volts). For example, asdepicted, when the second battery voltage 592 is greater than 13.3 volts(e.g., discharging 614 or auto-stop 616) the second DC/DC converter 414may step down the voltage. On the other hand, when the second batteryvoltage is less than 13.3 volts (e.g., discharging 618 and 619), thesecond DC/DC converter 414 may step up the voltage. Accordingly, asdepicted, the battery system voltage 588 is generally maintained at 13.3volts during this period.

Furthermore, the LTO/NMC battery 32 may continue to supply power untildepleted. For example, as depicted, the LTO/NMC battery 32 may supplypower during acceleration 620 until depleted and may supplement thelead-acid battery 30 to warm crank 622 the internal combustion engine.More specifically, both the lead-acid battery 30 and the LTO/NMC battery32 may be connected via the first DC/DC converter 412 and the secondDC/DC converter 414 to warm crank 622. As in the embodiments describedabove, the battery control unit 34 may determine whether to warm crankwith the lead-acid battery 30, the second battery 32, or both dependingon the state of charge of each battery and the minimum state of chargefor performing each vehicle operation (e.g., warm crank 622). Oncedepleted, the LTO/NMC battery 32 may be disconnected via the secondDC/DC converter 414 and the lead-acid battery 30 may be connected viathe first DC/DC converter 412 to enable the lead-acid battery 30 tosupply power.

Active Architecture—Voltage Matched

As described above, FIG. 20D describes an active battery system when thebatteries 30 and 32 are voltage matched. FIG. 201) depicts a batterysystem voltage curve 624, a lead-acid battery voltage curve 626, and asecond battery voltage curve 628. More specifically, the voltage curves624, 626, and 628 are based on the voltage characteristics described inFIG. 7. In other words, a lead-acid battery 30 and a LTO/LMO battery 32.Additionally, similar to the third partial voltage match embodimentdescribed in FIG. 20C, the lead-acid battery 30 may generally bemaintained between 95-100% state of charge and the LTO/LMO battery 32may be maintained generally at 0% state of charge even though the secondbattery voltage 628 is less than the threshold voltage to enable thesecond battery to utilize its full storage capacity to captureregenerative power.

Similar to the partial voltage match embodiment described in FIG. 20C,the lead-acid battery 30 supplies power to the electrical system 66 byitself during key-off 630, cold crank 632, acceleration 634, andcruising 636. During this period (e.g., between time 0 and time 3), thelead-acid battery voltage 626 may be stepped up to a constant voltage(e.g., 13.3 volts) by the first DC/DC converter 412 (e.g., boostconverter) and the LTO/LMO battery 32 may be maintained at approximately0% state of charge and disconnected via the second DC/DC converter 414.Accordingly, as depicted, the battery system voltage 624 remainsrelatively constant at 13.3 volts.

When regenerative power is generated (e.g., regenerative braking 638 or640), the alternator 64 outputs a constant voltage (e.g., 13.3 volts)and the lead-acid battery 30 is disconnected via the first DC/DCconverter 412, To charge the LTO/LMO battery 32, the second DC/DCconverter 414 may set the voltage (e.g., step down the bus voltage(e.g., 13.3 volts) to the second battery voltage (e.g., between11.7-13.2 volts)). Accordingly, as depicted, the battery system voltage624 is maintained at a relatively constant 13.3 volts, the lead-acidbattery voltage 626 is maintained at a relatively constant 12.9 volts,and the second battery voltage 628 increases as the LTO/LMO battery 32captures regenerative power.

When the LMO/LTO battery 32 supplies power to the electrical system 66(e.g., cruising 642 or auto-stop 644), the second DC/DC converter 414may maintain the bus voltage at approximately the same voltage output bythe alternator 64 (e.g., 133 volts) by stepping up the second batteryvoltage (e.g., 11.7-13.2 volts). Accordingly, as depicted, the batterysystem voltage 624 is maintained at a relatively constant 13.3 volts andthe second battery voltage 626 decreases as the LMO/LTO battery 32supplies power.

Furthermore, the LMO/LTO battery 32 may continue to supply power untildepleted. Once depleted, the LMO/LTO battery 32 may be disconnected viathe second DC/DC converter 414 and the lead-acid battery 30 may beconnected via the first DC/DC converter 412. Additionally, the firstDC/DC converter 412 steps up the lead-acid battery voltage 626 to matchthe voltage output by the alternator 64, According, as depicted, whenthe LTO/NMC battery 32 is depleted during auto-stop 644, lead-acidbattery voltage 626 decreases as the lead-acid battery 30 supplies powerand the battery system voltage 624 is maintained relatively constant at13.3 volts. Furthermore, since the LMO/LTO battery is depleted, thelead-acid battery 30 may supply power to cold crank 646 and duringacceleration 648. During these periods, the first DC/DC converter 412may continue stepping up the lead-acid battery voltage 626 to maintainthe battery system voltage 624 relatively constant.

Based on the various embodiments of the active battery systems 60described above, the control algorithm utilized by the battery controlunit 34 may be more complex than the algorithm utilized for semi-activebattery systems 58 and switch passive battery systems 56. Morespecifically, in addition to controlling the alternator 64, the batterycontrol unit 34 may control the operation of both the first DC/DCconverter 412 and the second DC/DC converter 414, which may includeopening/closing internal switches in each. For example, in someembodiments, the battery control unit 34 may utilize the DC/DCconverters 412 and 414 to enable the second battery 32 to be moreoptimally charged (e.g., with a higher charging voltage) whileprotecting the lead-acid battery 30 from overvoltage. Accordingly, thebattery control unit 34 may turn on/off the alternator 64 as well asopen/close the internal switches in the DC/DC converters 412 and 414 tomaintain each of the batteries 30 and 32 at their respective targetstates of charge. Additionally, the battery control unit 34 may controlother operational parameter with the DC/DC converters 412 and 414, suchas limiting current or voltage.

In each of the active battery system 60 embodiments described above, thebattery system voltage (e.g., 532, 558, 588, and 624) remains relativelyconstant during operation of the vehicle (e.g., time 0 to time 8). Morespecifically, in each of the embodiments, the second DC/DC converter 414is described as a bi-directional converter (e.g., boost-buck converter)to bi-directionally step up or step down voltage. For example, in thenon-voltage match embodiment described in FIG. 20A, the second DC/DCconverter 414 steps up the bus voltage to charge the second battery 32and steps down the second battery voltage to supply a constant voltage(e.g., 13.3 volts). However, as described above, DC/DC converters may beless than 100% efficient. Additionally, the cost of a bi-directionalconverter may be greater than a converter with a bypass path 418 asdescribed in FIGS. 16 and 17. Accordingly, the active battery systemembodiments described above may alternatively utilize a second DC/DCconverter 414 with a bypass path 418. Illustratively, in the non-voltagematch embodiment, the second battery 32 may discharge (e.g., duringcruising or auto-stop) via the bypass path 418 due to the highervoltage.

As described above, starting (e.g., cranking) the internal combustionengine 18 may require a significant amount of power. In someembodiments, the starter 62 may utilize 5 kW or more. However, DC/DCconverters capable of meeting such power requirements may be costly.Accordingly, FIG. 21 depicts an embodiment of a switch active batterysystem 650. As depicted, a switch 652 is included between the lead-acidbattery 30 and the bus 68, and a DC/DC converter 654 is included betweenthe second battery 32 and the bus 68. Thus, the switch 652 selectivelyconnects/disconnects the lead-acid battery 30 and the DC/DC converter654 selectively connects/disconnects the second battery 32. Morespecifically, the switch 652 is utilized because switches are generallyless costly and more robust by enabling more power to pass through whencompared to a DC/DC converter. Additionally, the switch 652 may beincluded to selectively connect the lead-acid battery 30 because thelead-acid battery may be capable of providing a larger amount of poweras compared to the second battery 32. Additionally or alternatively, theswitch 652 and the DC/DC converter 654 may be switched.

The described techniques enable improved power storage and powerdistribution efficiency for battery systems in vehicular contexts (e.g.,micro-hybrid and regenerative braking vehicles) as well as other energystorage/expending applications (e.g., energy storage for an electricalgrid). In some embodiments, the techniques described herein may increasefuel economy and/or reduce undesirable emissions by 3-5% as compared totraditional battery systems (e.g., a single 12 volt lead-acid battery)because the load on the alternator is reduced by more efficientlycapturing regenerative power, which may then be used to supplyelectrical power to the vehicle's electrical system 66 in place of thealternator (e.g., fuel energy).

More specifically, in some embodiments, the disclosed battery systemincludes a battery 30 and a second battery 32 that each utilizes adifferent battery chemistry (e.g., lead-acid or nickel manganese cobaltoxide). Additionally, the battery 30 and the second battery 32 arearranged in various parallel architectures such as passive,semi-passive, switch passive, semi-active, active, or switch active. Asdescribed above, the various architectures may provide varying levels ofcontrol over the battery system via switches and/or DC/DC converters.Based on the battery chemistries and architecture selected, the battery30 and the second battery 32 may operate in tandem. For example, thefirst battery 30 may be capable of supplying large amounts of currentwhile the second battery (e.g., power device) 32 may be capable ofefficiently capturing, storing, and distributing regenerative powerbecause of its higher coulombic efficiency and/or higher power chargerate. In other words, the first battery may be the primary source ofelectrical power and the second battery may supplement the firstbattery, which may also enable a reduction in the battery's storagecapacity. Furthermore, the batteries utilized in the battery system maygenerally conform with a traditional battery system by outputtingvoltages ranging between 7-18 volts.

While only certain features and embodiments of the invention have beenillustrated and described, many modifications and changes may occur tothose skilled in the art (e.g., variations in sizes, dimensions,structures, shapes and proportions of the various elements, values ofparameters (e.g., temperatures, pressures, etc.), mounting arrangements,use of materials, colors, orientations, etc.) without materiallydeparting from the novel teachings and advantages of the subject matterrecited in the claims. The order or sequence of any process or methodsteps may be varied or re-sequenced according to alternativeembodiments. It is, therefore, to be understood that the appended claimsare intended to cover all such modifications and changes as fall withinthe true spirit of the invention. Furthermore, in an effort to provide aconcise description of the exemplary embodiments, all features of anactual implementation may not have been described (i.e., those unrelatedto the presently contemplated best mode of carrying out the invention,or those unrelated to enabling the claimed invention). It should beappreciated that in the development of any such actual implementation,as in any engineering or design project, numerous implementationspecific decisions may be made. Such a development effort might becomplex and time consuming, but would nevertheless be a routineundertaking of design, fabrication, and manufacture for those ofordinary skill having the benefit of this disclosure, without undueexperimentation.

1-20. (canceled)
 21. An automotive battery module having dual voltagecomprising: a housing; a plurality of battery cells connected to formbattery cell blocks disposed in the housing; a battery control unitconfigured to control operation of a battery system, the battery systemincluding at least one switching device operably connected to a firstbattery cell block in a first connection arrangement, the first batterycell block configured to deliver a first voltage, the at least oneswitching device operably connected to a second battery cell block in asecond connection arrangement, the second battery cell block configuredto deliver a second voltage, the battery control unit disposed in thehousing; and a plurality of terminals on the housing and electricallycoupled to the battery control unit and plurality of battery cells,providing an external electrical connection to deliver the first voltageand the second voltage.
 22. The battery module of claim 21, wherein thehousing is a multi-part housing.
 23. The battery module of claim 22,wherein the multi-part housing comprises a container and a lid.
 24. Thebattery module of claim 21, wherein the housing is a single continuoushousing.
 25. The battery module of claim 21, wherein the first batterycell block utilizes a first battery chemistry.
 26. The battery module ofclaim 21, wherein the second battery cell block utilizes a secondbattery chemistry different from the first battery chemistry.
 27. Theautomotive battery module of claim 21, wherein: the first batterychemistry is a lithium nickel manganese cobalt oxide battery chemistry,a lithium nickel cobalt aluminum oxide battery chemistry, a lithiumnickel manganese cobalt oxide-lithium nickel cobalt aluminum oxidebattery chemistry, a lithium-titanate/lithium nickel manganese cobaltoxide batter chemistry, a nickel-metal hydride battery chemistry, or alithium iron phosphate battery chemistry; and the second batterychemistry is a lead-acid battery chemistry.
 28. The automotive batterymodule of claim 21, wherein: the first battery cell block is configuredto store electrical energy using a first electrochemical reaction; andthe second battery cell block is configured to store electrical energyusing a second electrochemical reaction different from the firstelectrochemical reaction.
 29. The battery module of claim 21, whereinthe battery cells are connected in series.
 30. The battery module ofclaim 21, wherein the battery cells are connected in parallel.
 31. Thebattery module of claim 21, wherein the first battery cell block and thesecond battery cell block are connected by a parallel architectureselected from the group consisting of passive, semi-passive, switchpassive, semi-active, or active.